public Color toSepia() {
        float r = ShaderUtils.clamp(this.rgba[0] * 0.393f + this.rgba[1] * 0.769f + this.rgba[2] * 0.189f, 0, 1);
        float g = ShaderUtils.clamp(this.rgba[0] * 0.349f + this.rgba[1] * 0.686f + this.rgba[2] * 0.168f, 0, 1);
        float b = ShaderUtils.clamp(this.rgba[0] * 0.272f + this.rgba[1] * 0.534f + this.rgba[2] * 0.131f, 0, 1);
        return new Color(r, g, b, this.rgba[3]);
    }
Helper class for working with colors and gradients

@author Anthyon
jme3-terrain/src/main/java/com/jme3/terrain/noise/Color.java