#64748B on white
Tailwind slate-500 — roughly Slate — measured against white to WCAG 2.2 and APCA.
4.76:1
contrast ratio · APCA Lc 70
The quick brown fox
…and the same at 13 px
…and the same at 13 px
✓ Body text (AA, 4.5:1)
✕ Body text (AAA, 7:1)
✓ Large text (AA, 3:1)
✓ Borders and icons (1.4.11, 3:1)
Where you can use it
#64748B clears AA on white, so it works for body copy at any size. It also clears the 3:1 required of borders, icons and focus rings.
Under colour blindness
Contrast is a lightness relationship, so a ratio survives colour blindness — but the pair can still lose the distinction it was carrying. This is the same two colours as seen with each dichromacy.
| Vision | Foreground | Background | Ratio |
|---|---|---|---|
| Normal | #64748B |
#FFFFFF |
4.76:1 |
| Protanopia red-blind, ~1% of men |
#6B6B86 |
#FFFFFF |
5.16:1 |
| Deuteranopia green-blind, ~6% of men |
#6A6985 |
#FFFFFF |
5.29:1 |
| Tritanopia blue-blind, rare |
#658281 |
#FFFFFF |
4.15:1 |
What the thresholds mean
- 4.5:1 — WCAG 2.2 success criterion 1.4.3, the minimum for body text.
- 3:1 — the minimum for large text (18.66 px bold or 24 px regular) and, under 1.4.11, for any non-text thing you have to perceive: input borders, icons, focus indicators.
- 7:1 — AAA, criterion 1.4.6.
- APCA Lc 70 — a perceptual model that accounts for polarity, so dark-on-light and light-on-dark are not treated as the same problem. It is the direction WCAG 3 is heading and it disagrees with the ratio often enough to be worth reading alongside it.
Related
One passing pair is not a system
ColorsMine checks every pairing a palette implies, in light and dark, and names the single change that moves the grade most.
Open ColorsMine