If you have a color vision deficiency, there is no trick that will make you see the hidden numbers on a screening test. The plates are specifically designed to be impossible to guess your way through. But depending on the severity of your deficiency and the reason you need to pass, you have more options than you might think, from alternative tests that measure what you can do rather than what you can’t, to optical aids that shift the odds, to career pathways that accept mild deficiencies.
How Color Vision Tests Actually Work
Most screening uses pseudoisochromatic plates, the classic dotted circles where you identify a number hidden in a pattern of colored dots. The Ishihara test is the most common version, but the Hardy-Rand-Rittler (HRR) plates work on the same principle. These tests use four different plate designs, and understanding them explains why memorization alone won’t help.
Vanishing plates show a number that people with normal color vision read easily but that disappears for color-deficient observers. Transformation plates embed two different numbers in the same background: one visible to normal eyes, another visible only to color-deficient eyes. So you’ll read a number confidently, but it’s the wrong number. Hidden plates flip the script entirely, showing a figure that only color-deficient observers can see. Diagnostic plates display a colored number on a gray background to determine whether your specific deficiency is protan (red-weak) or deutan (green-weak).
Because the test uses multiple plate types with contradictory designs, memorizing the “correct” answers from an online chart will actually make your results look suspicious. You’d get the vanishing plates right but then fail to report the hidden digits that a truly normal eye wouldn’t see. Trained examiners catch this pattern quickly.
Why Online Practice Tests Won’t Help
Practicing Ishihara plates on a screen is unreliable for a simple reason: your monitor’s brightness, color calibration, and viewing angle all change how the dots appear. A plate that stumps you on one screen might look obvious on another. Clinical tests use standardized booklets viewed under controlled lighting, or increasingly, validated computer-based systems with strict calibration requirements. The FAA, for example, now requires that all pilot color vision screening use approved computer-based tests performed in person. Virtual testing, downloaded versions, and printed copies are explicitly prohibited.
So even if you memorize every plate online, the version you encounter in a clinical or occupational screening will likely use different plate sets, different lighting, or an entirely different test format.
Color-Correcting Glasses and Contact Lenses
Optical aids are the most commonly searched workaround, and they deserve a realistic explanation. Two main options exist: filter glasses (like EnChroma) and monocular red-filter contact lenses (like the X-Chrom lens).
EnChroma-style glasses work by filtering out specific wavelengths of light where red and green signals overlap, increasing the contrast between those colors. Optical modeling suggests they can increase red-green discriminability by roughly 25 to 37 percent depending on your type of deficiency, with the largest benefit going to people with mild green-weak (deuteranomalous) vision. However, clinical studies have not demonstrated consistent, dramatic improvements on standardized screening tests. The glasses change how colors look, but they don’t restore normal color processing in your brain.
The X-Chrom contact lens takes a different approach. It’s a deep red filter worn on one eye, which creates a brightness difference between your two eyes when looking at colors that would otherwise blend together. Research confirms it can improve color-naming ability and boost scores on certain plate tests. The catch: it doesn’t correct your color vision in real-world conditions, and many occupational screening programs specifically prohibit tinted lenses or glasses during testing. If the examiner checks or the testing protocol requires unaided vision, this option is off the table.
Alternative Tests That Measure Severity
Here’s the most practical piece of information for many readers: failing an Ishihara screening is not always the end of the road. Many employers and licensing bodies use a tiered system. You fail the initial screen, then take a more detailed test that measures how severe your deficiency actually is. If it’s mild enough, you pass.
The Farnsworth D-15 test is the most common second-tier assessment. Instead of reading hidden numbers, you arrange 15 colored caps in order. The test was specifically designed to separate “safe” from “unsafe” color-deficient individuals for occupational purposes. If you arrange the caps without making errors that cross the hue circle (meaning you don’t confuse colors that are far apart), you’re classified as having a mild deficiency. Many safety-critical jobs accept a D-15 pass even after an Ishihara fail.
The Farnsworth-Munsell 100 Hue test is a more detailed version with 85 colored caps. Your result is a Total Error Score. A score of 100 or below passes 95 percent of people with normal vision, but it also passes about 24 percent of people with congenital color deficiencies. Among those with mild deficiencies who score under 100, roughly 30 percent still show some red-green discrimination weakness on closer analysis, but their overall score is within the acceptable range.
What Specific Jobs Actually Require
The requirements vary enormously, and knowing exactly what your target employer or licensing body accepts can change your strategy completely.
Aviation: As of January 2025, the FAA uses computer-based color vision tests with specific numerical cutoffs. On the Waggoner test, for instance, you need a general score of 21 out of 25. On the Rabin Cone Test, you need 55 or higher for each color channel (red, green, and blue), tested in each eye separately. The CAD test allows a red-green score up to 6 for deutan deficiency and up to 12 for protan deficiency before you fail. These thresholds mean that mild to moderate deficiencies can sometimes pass depending on the specific test offered.
Firefighting: UK fire service standards illustrate a common pattern. You take the Ishihara first. If you fail, you take the D-15 test. If you pass the D-15, meaning your deficiency is mild, you may still qualify. The exception is protan (red-weak) deficiency: even mild protanomalous individuals are excluded from firefighting in the UK because reduced red sensitivity affects the ability to see flames and red-coded safety equipment. Mild deutan (green-weak) individuals who pass the D-15 are considered safe to work.
Military and law enforcement: Requirements vary by branch and country, but many follow the same tiered approach. A complete Ishihara fail doesn’t always disqualify you if you pass an alternative test.
Strategies That Actually Improve Your Chances
You can’t change your cone cells, but you can optimize the conditions around testing.
- Request the right alternative test. If you fail an Ishihara, ask which secondary tests are accepted. The D-15, anomaloscope, or lantern tests measure different aspects of color vision, and your deficiency may be mild enough to pass one even if you can’t pass another. Some licensing authorities let you choose from a list of approved alternatives.
- Test under optimal conditions. Fatigue, medication, and poor lighting can worsen color discrimination. Schedule your test for a time when you’re well-rested. Clinical testing should use daylight-equivalent illumination, but if you notice the room is dim or the lighting has a yellow cast, it’s reasonable to mention this.
- Know your specific deficiency type. Get a proper diagnostic evaluation before your occupational screening. Knowing whether you’re protan or deutan, and whether your deficiency is mild or severe, lets you research exactly which jobs and which tests are realistic for you. A mild deuteranomalous deficiency opens far more doors than a complete dichromatic deficiency.
- Check if your employer allows optical aids. Some testing protocols permit color-filter lenses, others don’t. If they’re allowed, the X-Chrom lens or similar filters can meaningfully improve plate-test performance.
When the Deficiency Is Too Severe
Complete dichromats (people missing one cone type entirely) will fail virtually all occupational color vision screenings for safety-critical roles. No glasses, contact lenses, or test-taking strategies will overcome a severe deficiency on a properly administered test. The D-15 test catches severe deficiencies reliably, and the error pattern is unmistakable to the examiner.
If your deficiency is severe, the most productive path is identifying which specific roles within your target field don’t require color vision certification, or which alternative career tracks exist. Many aviation roles outside the cockpit, technical positions in fire investigation rather than active firefighting, and numerous military specialties have no color vision requirement at all.