MRCS

Multi-Ramp Coloring Scheme

Abstract

MRCS (Multi-Ramp Coloring Scheme) is a simple and minimalistic color scheme generator, designed by Dr. Ralf S. Engelschall. It expands a few base colors into full color ramps for use in applications, websites, diagrams, etc.

MRCS is based on the following foundational rules:

1. Tone Preservation: A base (usually RGB) color is converted into the perceptually uniform OKLCH color space, where its chroma (C) and hue (H) are the tone of the color and are kept fixed for the entire ramp.

2. Lightness Sweep: Only the lightness (L) of OKLCH is swept, in equal steps, between a floor and a ceiling bound. Color 1 sits exactly at the floor bound and color N sits exactly at the ceiling bound.

3. Grey Exception: By default, a plain grey base color (OKLCH chroma below 0.01) spans the entire lightness range (L 0%...100%), while a chromatic base color stays off both of its ends (L 20%...90%), as a chromatic color degenerates towards black and white.

4. Complement Transposition: A base color optionally is transposed into its complement on the color wheel, by rotating its OKLCH hue by 180 degrees while keeping its lightness and chroma. A plain grey base color has no hue and hence is its own complement.

5. Gamut Mapping: As a fixed chroma is not reachable at every lightness, the chroma is reduced just enough to re-enter the sRGB gamut, which leaves the lightness and the hue of a color untouched.

Installation

$ npm install [-g] @rse/mrcs

Usage

MRCS can be used from the command-line via its CLI.

Specify one or more color ramp specifications of the format <name>:<rgb>[^][+<floor>][-<ceiling>][/<count>], where <rgb> is any CSS color notation -- the short hex #rgb, the long hex #rrggbb, a color name like cornflowerblue, or a functional notation like rgb(51, 102, 204), hsl(220, 60%, 50%), or oklch(53% 0.17 262) -- ^ transposes the base color into its complement, <floor> is the lower lightness bound in percent, <ceiling> is the inset below white of the upper lightness bound in percent, and <count> is the number of colors (default: 9).

Choose an output format (css, root, json, yaml, or url) and an optional CSS variable name prefix:

$ mrcs --prefix mrcs --format root "grey:#808080/5" "blue:#3366cc/5"
:root {
    --mrcs-grey-1: #000000;
    --mrcs-grey-2: #222222;
    --mrcs-grey-3: #636363;
    --mrcs-grey-4: #aeaeae;
    --mrcs-grey-5: #ffffff;
    --mrcs-blue-1: #001040;
    --mrcs-blue-2: #053598;
    --mrcs-blue-3: #386bd2;
    --mrcs-blue-4: #75a4ff;
    --mrcs-blue-5: #cddfff;
}

$ mrcs --format yaml "blue:#3366cc/3" "blue-comp:#3366cc^/3"
blue:
    - "#001040"
    - "#386bd2"
    - "#cddfff"
blue-comp:
    - "#1f1400"
    - "#916a0c"
    - "#ffd891"

The entire color scheme can be collapsed into the compact URL notation mrcs:<spec>,<spec>[,...], which is accepted back as a single positional argument. In this notation all defaults are resolved, the base color is canonicalized to a hex color notation without its leading #, and the complement transposition is already applied:

$ mrcs --format url "grey:#808080/5" "blue:#3366cc^"
mrcs:grey:808080+0-0/5,blue:8c6500+20-10/9

$ mrcs --format yaml "mrcs:grey:808080+0-0/5,blue:8c6500+20-10/9"
grey:
    - "#000000"
[...]

Alternatively, MRCS can be used programmatically via its TypeScript/JavaScript API, which knows only the color ramp itself and neither the name nor the prefix of a color:

import { parse, format, generate } from "@rse/mrcs"

/*  parse a color ramp specification (resolving all defaults)  */
const spec = parse("#3366cc")
/*  { rgb: "#3366cc", floor: 20, ceiling: 10, count: 9 }  */

/*  the "^" suffix transposes the base color into its complement  */
parse("#3366cc^")
/*  { rgb: "#8c6500", floor: 20, ceiling: 10, count: 9 }  */

/*  format a specification back into its canonical string notation  */
format(parse("#3366cc^"))
/*  "#8c6500+20-10/9"  */

/*  generate the color ramp of a specification  */
generate(parse("#3366cc/5"))
/*  [ "#001040", "#053598", "#386bd2", "#75a4ff", "#cddfff" ]  */

generate(parse("#808080/5"))
/*  [ "#000000", "#222222", "#636363", "#aeaeae", "#ffffff" ]  */

License

Copyright © 2026 Dr. Ralf S. Engelschall (http://engelschall.com/)

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.