combinatorics – What is the probability of observing unique colors in a combinatorial problem?

Suppose I have $K$ colors and for each color there are $N$ balls, so there are $K*N$ balls in total. Now I draw $M$ balls from them. For these $M$ balls, some balls have the same color and some don’t. Let $K_u$ be the number of colors that are unique in the $M$ balls. My question is: what is the expectation of $K_u/K$?