What does the color black symbolize when children color with it?

when children draw with black they are drawing with black?

There are many people who will assume that a child using a black crayon or paint is expressing anger, depression or some other deep/strong emotion. This is not necessarily true.
Most children are drawn to intense colours. The choice of a colour is very much individual.
If you want to know why someone (even a child) is using a specific colour the best way to find out is to ask... certainly with young children, one must use simple language, but it is possible to find out.
Do not assume any child psychology book has all the answers. It has been my experience, the only way to rely on ONE child psychology book over another is to be sure the child has read the same one you are using.