Minecraft wiki entry for Procedural_animated_texture_generation, associated text: Calculates a color_heat as double the soup_heat clamped between 0 and 1 inclusive.
Then it calculates the color components of the pixel as follows:
float red = color_heat * 100F + 155F
float green = color_heat^2 * 255F
float blue = color_heat^4 * 128F