For different using areas, it always request different color cable duct, in order to match the pannel color or the ouside evironment color, makes all the thing harmony. But the wide used color is gray, as the cabnet main color is gray, the second one is white, third one is black, for black conmunicate pannel using. And the blue color duct always used in oil projects, some times, they use orange color,for these colors are easy and convenient to know where the cables put, and have to take care about the cables.