Add some painted patterns to the wooden slices before you varnish them
Remember earlier we mentioned that you could repurpose old tree branches to make cup placeholders? You can have both if you like the rustic look but would like to add a pop of color. You can use acrylics or other paints to draw on any design you want, but make sure to do so before you varnish the pieces.
If you tried to do it over varnish, you would quickly realize that the paint does not want to stick to a smooth surface. Raw wood is porous, which makes it a much better canvas for the pigments to grab onto.