it can depend of the artist, but i guess you have experience the point when you are confused with colors. Though the metod to fix this can be different for everyone; in my case i sometimes make the artworks in a basic way and in gray scale, and then with the help of colors and overley i put some colors in it. Though just with that it is not enough, it could help as the bones, with that is working with the details and adding some variations with the colors ^^