Technological skills for art include use of color, but art is often in black-and-white. What does it say about the list of skills?

A. They are designed to exclude black-and-white photography.
B. They are only meant for artwork that contains a lot of color.
C. They are meant to apply the color paintings not other forms of art
D. They are more guidelines than rules meant to apply to every piece.

D. They are more guidelines than rules meant to apply to every piece.