Lori, if you have flat sided doors and they are made with luan plywood, I would paint them. That is a naturally darkish colored wood and it doesn't have much grain pattern. I had those and replaced a few of the more visible ones with flat sided doors that had oak faced plywood. The oak does cost a little more than luan plywood and is much more attractive finished. You have a fair amount of possible color range with stains that will still allow you to see the natural grain.
If you have multi-paneled doors, the cost of these is a lot more, as are the possibilities. But the wood that they are made from will control what you can do about lightening the color and how you will have to go about it. The "natural wood color" for birch, ash, and walnut are quite different from each other. Tell us more about what you have.