Im not sure if you are trying to do harlequin paint, but either way, you need more white in the highlights you are brushing. using this as a paint refrence
Also, I noticed your selections are very hard/ alot of jagged selection.
If you are using lasso tool, you can use the 'Refine Edge' function or if you are using pentool give it a 0.3px feather when selecting area so it is nice and soft edges
Yours ontop/ mine below