#64748B on black
Tailwind slate-500 — roughly Slate — measured against black to WCAG 2.2 and APCA.
4.41:1
contrast ratio · APCA Lc 32
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)
The nearest colour that passes
Keeping the hue and moving only the lightness, #67778E is the closest shade to #64748B that clears 4.5:1 on black — at 4.61:1.
#64748B4.41:1 — fails
#67778E4.61:1 — passes
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 |
#000000 |
4.41:1 |
| Protanopia red-blind, ~1% of men |
#6B6B86 |
#000000 |
4.07:1 |
| Deuteranopia green-blind, ~6% of men |
#6A6985 |
#000000 |
3.97:1 |
| Tritanopia blue-blind, rare |
#658281 |
#000000 |
5.06:1 |
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 32 — 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
Fixing one pair is not the job
ColorsMine checks every pairing a palette implies, in light and dark, and names the single change that moves the grade most.
Open ColorsMine