Tide Pool
Open in tool →Sea-green and slate with a coral — a literal tide pool: two cool tones, one warm creature.
Color
#21213b
#21213b
hex
#21213brgb
rgb(33, 33, 59)hsl
hsl(240, 28%, 18%)oklch
oklch(0.261 0.048 282.5)Closest name: Eclipse Elixir (#1f2133)Relative luminance 0.0173
Colors that go with #21213b
Charcoal, Dark Olive Green and Sienna lead the list. Each partner is a real named colour with the reason it works — a wheel relationship, a neutral that carries it, or a pairing lifted from a palette or brand system that actually shipped — and every pair opens in the palette tool.
Charcoal #36454f
neutralshippedCharcoal is the text near-black for #21213b: softer than #000 and cool enough to feel like part of the same palette.
Dark Olive Green #556b2f
complementaryshippedDark Olive Green sits directly opposite #21213b on the wheel — the strongest contrast one hue can give another, so use it small: a button, a link colour, one highlight.
Sienna #a0522d
split-complementshippedSienna is a split-complement of #21213b: nearly opposite, so it still pops against it, without the vibrating edge of a true complement.
Slate Blue #6a5acd
analogousshippedSlate Blue is #21213b's neighbour on the wheel, so the two read as one family — use it for hover states, gradients and secondary surfaces.
Steel Blue #4682b4
analogousshippedSteel Blue is #21213b's neighbour on the wheel, so the two read as one family — use it for hover states, gradients and secondary surfaces.
Teal #008080
triadicshippedTeal completes a triad with #21213b — three hues spaced evenly round the wheel, the classic way to get energy into a palette without a clash.
Amber #ffbf00
shippedAmber is paired with #21213b in 18 real palettes, including Beach Hut and Southwest Airlines's brand system, as the supporting colour.
Blue #0000ff
shipped23 real palettes, including Monzo's brand system and Sketch's brand system put Blue beside #21213b, as the accent.
Real palettes that use #21213b
Tints & shades
Harmonies
Contrast
| #21213b as text | Ratio | AA | AA large | AAA | Fix |
|---|---|---|---|---|---|
Aaon white | 15.61:1 | pass | pass | pass | Passes AAA — no fix needed. |
Aaon black | 1.35:1 | fail | fail | fail |
Fixes keep hue and saturation and move lightness only, so the suggestion stays on-brand. Ratios are symmetric: the same numbers apply with #21213b as the background.
Brands using this color
Palettes built around it
Fonts for this mood
#21213b reads as cool, muted, dark. The font library is tagged with the same vocabulary:
mcpConnect your agent — build around #21213b
live endpointPoint any MCP client at the shared colors endpoint and your agent gets the same engine as this page — direct_palette, edit_direction, check_palette, check_contrast — read-only, no key. Every direction it proposes comes with a /colors/d/… link: open it, lock what you like, paste the link back, and the agent edits rather than re-rolls.
endpoint
https://mcp.brandsweets.com/colors/mcpclaude mcp add --transport http brandsweets-colors https://mcp.brandsweets.com/colors/mcp
try this prompt
›analyze #21213b and generate a 5-color palette that keeps it as the primary; give me the /palettes/new link
tool url
/palettes/new/21213b-a19cc4-df994e-251f2d-e9edf1?lock=0&style=vibrantWant the agent to remember your picks and write them into a living brand? Create a free BrandSweets workspace.
Machine-readable: color.md