I am going to try making milk paint with natural pigments for adding some color to the Dulcimer I'm working on.
It has survived since ancient Egypt, and was also used by the pioneers on Colonial furniture.
It has the effect of adding soft color while remaining translucent, so you can see the grain of the wood through it.
Here is a link for a milk paint recipe, followed by a link to a site that has an extensive list of natural pigments you can forage, grouped by color.
I have dried some grass so far as well as dandelion flowers.