Algorithm to create heatmap colors

Colour.php

<?php


class Colour
{

    /**
     * Maps a float value to a CSS HSL color
     *
     * 0    : blue
     * 0.25 : cyan
     * 0.5  : green
     * 0.75 : yellow
     * 1    : red
     *
     * @param float $value         a value between 0 and 1 inclusive
     * @param int   $max_hue_angle default 240, for blue > cyan > green > yellow > red gradients
     *
     * @return string a CSS HSL() color definition string
     */
    public static function valueToHSLColour(float $value, int $max_hue_angle = 240): string
    {
        if ($max_hue_angle < 0 || $max_hue_angle > 360) {
            throw new \InvalidArgumentException('max_hue_angle must be between 0 and 360 inclusive');
        }
        if ($value < 0 || $value > 1) {
            throw new \InvalidArgumentException('value must be between 0 and 1 inclusive');
        }

        $hue = (1.0 - $value) * $max_hue_angle;
        return sprintf("hsl(%d, 100%%, 50%%)", $hue);
    }

}