1. He is yellow. = He is cowardly.

2. He is blue. = He is sad.

3. He is green. = He is inexperienced.

4. He is seeing red. = He is very angry.

5. That is a white lie. = That is a little lie that will not hurt anyone. For example, you tell your girlfriend that her ugly hat is "beautiful."

A chicken is yellow so normally calling someone yellow implies that they are "chicken" or afraid.  It has nothing whatsoever to do with skin color.