lib/rgb.js
function to_rgb(obj){
    return [obj.R, obj.G, obj.B].map(format_number).join('');
}
function to_rgb(obj){
    return [obj.R, obj.G, obj.B].map(format_number).join('');
}
function to_rgb ( obj ) { return [ obj . R , obj . G , obj . B ] . map ( format_number ) . join ( '' ) ; }
reversed method of `rgb_2_object`
reversed method of rgb_2_object