Here are some examples of more or less how the shine on Spark’s hair should look. 
It should not look like this: we are not going for the “two toned” look as in she has red and brown strands growing out of her head, but instead one solid color of brown that shimmers bright red.
I need to work on this. @_@ In my head, her hair is still mahogany or really dark red (if my Draw Something doodles are any indication!) of course, I need to work on coloring in general!