Method to use the populated region list to colour our texture via height map values.

planetGen_regionColour.cs

void ColourIt()
{
    // COLOUR!

    // Colour in elevations
    
    // _stride - is the size in bytes of the width of the texture RGBA = 4bytes * width of texture.
    // _textureSize - size (w & h) in pixels of the texture.

    for (int y = 0; y < _textureSize; y++)
    {
        for (int x = 0; x < _stride; x+=_bytesPerPixel)
        {
            double value = (double)_heightmapBuffer[index + x];

            for (int r = 0; r < _regions.Count; r++)
            {
                if (value >= _regions[r].range[0] && value < _regions[r].range[1])
                {
                    double top = _regions[r].range[1] - _regions[r].range[0];

                    // A little formula to shift the colour so we get a nice little ramp.
                    double shift = ((1.0 - ((value - _regions[r].range[0]) / top)) * 20.0);

                    double B = _regions[r].baseColor.B - shift;
                    double G = _regions[r].baseColor.G - shift;
                    double R = _regions[r].baseColor.R - shift;

                    // Clamp the values.
                    if (B < 0) B = 0;
                    else if (B > 255) B = 255;

                    if (G < 0) G = 0;
                    else if (G > 255) G = 255;

                    if (R < 0) R = 0;
                    else if (R > 255) R = 255;
                   
                    // Add colour to the destination texture.
                    _colourBuffer[index + x + 0] = (byte)B;
                    _colourBuffer[index + x + 1] = (byte)G;
                    _colourBuffer[index + x + 2] = (byte)R;
                    _colourBuffer[index + x + 3] = 255;
                }
            }
        }

        index += _stride;
    }
}