Color manipulation library

color.js

// Internal color conversion
// Converts `#ffffff` to `(255, 255, 255)`
function _colornum(color) {
    var l = color.length;
    return [
        parseInt(color.slice(l-6,l-4), 16),
        parseInt(color.slice(l-4,l-2), 16),
        parseInt(color.slice(l-2,l-0), 16)
    ];
}


// Sample usage:
//
//        gradient(0.4, ((-1, '#ff0000'), (0, '#ffffff'), (1, '#00ff00')))
//
// interpolates 0.4 between -1 - 0 - +1 and returns an in-between color
// as #RRGGBB
function gradient(x, ranges) {
    if (x <= ranges[0][0]) { return ranges[0][1]; }
    if (x >= ranges[ranges.length-1][0]) { return ranges[ranges.length-1][1]; }
    for (var i=0, range; range = ranges[i]; i++) {
        var start = range[0], color = range[1];
        if (x < start) { break; }
    }
    var p = (x - ranges[i-1][0]) / (ranges[i][0] - ranges[i-1][0]);
    var a = _colornum(ranges[i-1][1]);
    var b = _colornum(ranges[i][1]);
    return 'rgb(' +
        Math.round((a[0]*(1.0-p) + b[0]*p)) + ',' +
        Math.round((a[1]*(1.0-p) + b[1]*p)) + ',' +
        Math.round((a[2]*(1.0-p) + b[2]*p)) + ')';
}


// Some standard gradients
// --------------------------------------------------------------------------
RYG   = [[ 0.0, '#ff0000'], [0.5, '#ffff00'], [1.0, '#00ff00']]
RYG_1 = [[-1.0, '#ff0000'], [0.0, '#ffff00'], [1.0, '#00ff00']]

For good palettes, visit http://colorbrewer2.org/