That is a really good idea. I never would have thought of that for camparison. I'll try getting in the habit of comparing my colors with some of the amazing work on this site. Thanks.

I've had the same problem, and continue to. 
One technique I use now is to--when I feel I'm finished with my drawing--take an artwork from this site (such as from the weekly showcase) and place it right beside my finished work. That way, through comparison, it becomes clear if my piece is suffering from low contrast or washed-out colors.
 

I see what you mean. Thanks for the advice. Choosing colors is definitely a thing I struggle with. 

It looks a bit washed out. Could use more vibrancy/contrast.