I have had this problem also. The problem hasn't gone away but has gotten better with a couple things I have tried.
1. More than 1 wash with starting with a dark color than hitting some other areas with one a little lighter. I do this on an acrylic base because the oil paint doesn hurt it.
2. same thing with drybrushing but this is much harder to get right for me when trying to get it to look like wood. I use colors a lot closer to the color of the base coat than I do with the washes. I usually overdo the drybrushing then wipe some off which you can do with oils pretty easily.
Someday I hope I get this right, but this is working to some extent so far.