maratoolContrast checker vs color blindness simulator
A side-by-side comparison of Color Contrast Checker (WCAG) and Color Blindness Simulator.
A contrast checker measures the luminance ratio between two colors and tells you whether it passes WCAG AA (4.5:1 for body, 3:1 for large text) or AAA (7:1 and 4.5:1). A color blindness simulator shows how a palette appears under different vision deficiencies — deuteranopia, protanopia, tritanopia, achromatopsia.
Both matter; they catch different bugs. A red-on-green warning may have great contrast and still be invisible to a deuteranope. A pale-grey-on-white footer may be readable to a colorblind user and still fail WCAG.
When to use Color Contrast Checker (WCAG)
Use the contrast checker for every text-on-background pairing in your design — body copy, links, buttons, form labels, error messages. WCAG AA is the legal/practical floor; AAA is the comfort target for body text.
When to use Color Blindness Simulator
Use the color blindness simulator when meaning is conveyed by hue — status indicators (red/green), category colors in charts, traffic-light dashboards. Make sure the information survives when red and green collapse to similar yellows.
Side-by-side comparison
| Color Contrast Checker (WCAG) | Color Blindness Simulator | |
|---|---|---|
| Measures | Luminance contrast ratio | Perceptual hue shift |
| Output | Number (e.g. 4.7:1) + pass/fail | Re-rendered palette per condition |
| Standard | WCAG 2.1 / 2.2 | Brettel / Viénot / Machado models |
| Catches low contrast | Yes | No |
| Catches hue collisions | No | Yes |
| Typical use | Text-on-background pairs | Category colors, status indicators, charts |
| Affected users | Low vision, low-contrast environments | ~8% of men, ~0.5% of women (CVD) |
| Both required? | For text legality | For meaning conveyed by color |
Bottom line
Contrast checker for readable text; color blindness simulator for meaningful color. Ship a design only when it passes both — they catch different failures.
Frequently asked questions
Is WCAG AA enough?
AA is the legal floor in most jurisdictions and a practical default. AAA gives more headroom but constrains palettes hard. Aim AA for the whole interface and AAA for long-form body text where you can.
Which color blindness types should I check?
Deuteranopia (most common, ~6% of men) catches the majority of issues. Protanopia and tritanopia are rarer; achromatopsia is extreme but a great stress test — if it still works in greyscale, hue is not load-bearing.
Does dark mode change contrast requirements?
No — the WCAG ratios are symmetric (contrast is the same regardless of which color is on top). But many designs that pass in light mode quietly fail in dark mode; check both explicitly.
My link is blue on white — do I still need an underline?
Yes if the only signal is color. WCAG SC 1.4.1 forbids using color alone to convey meaning. Underlines, icons, or weight changes are the standard secondary signal.