Color

#b50306

#b50306
hex#b50306
rgbrgb(181, 3, 6)
hslhsl(359, 97%, 36%)
oklchoklch(0.487 0.198 28.7)
Closest name: All Systems Red (#b30103)Relative luminance 0.099

Colors that go with #b50306

Royal Blue, Steel Blue and Teal 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.

Tints & shades

Every swatch is its own page — click any to analyze it.

Harmonies

Complementary

Open in tool →

#03b5b2

#b5035f · #b55903

#06b503 · #0306b5

Split-complementary

Open in tool →

#03b559 · #035fb5

#5fb503 · #03b5b2 · #5903b5

Contrast

#b50306 as textRatioAAAA largeAAAFix
Aaon white
7.05:1passpasspassPasses AAA — no fix needed.
Aaon black
2.98:1failfailfail
  • AA: use #ec0407 as the text (4.59:1)
  • AAA: use #fd6366 as the text (7.15:1)
  • AA: or shift the background to #cfcfcf (4.52:1)
  • AAA: or shift the background to #ffffff (7.05:1)

Fixes keep hue and saturation and move lightness only, so the suggestion stays on-brand. Ratios are symmetric: the same numbers apply with #b50306 as the background.

Brands using this color

Fonts for this mood

#b50306 reads as warm, vivid, playful. The font library is tagged with the same vocabulary:

mcpConnect your agent — build around #b50306
live endpoint

Point 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.

endpointhttps://mcp.brandsweets.com/colors/mcp
claude mcp add --transport http brandsweets-colors https://mcp.brandsweets.com/colors/mcp
try this prompt

analyze #b50306 and generate a 5-color palette that keeps it as the primary; give me the /palettes/new link

tool url/palettes/new/b50306-c4a09c-62cb96-2d251f-f1e9ed?lock=0&style=vibrant

Want the agent to remember your picks and write them into a living brand? Create a free BrandSweets workspace.

Machine-readable: color.md