You might be getting the "crayon" impression because of all the white showing through (as you are using a low opacity brush). You could try fiddling with the background or parts of it. Perhaps adjust the white slightly to a warmer colour or a subtle green. Or even try a paper type background.
You could also try throwing down a texture on top (something I do) - a paper or rust or whatever texture on top of everything on a separate layer set to 10% overlay or thereabouts.