It can be risky and I really don't care for stain (like a box of chocolates, you never know what your gonna get) but one could sand off the varnish finish and apply a little walnut or darker stain. Sometimes it turns out good and some times no so much.

That's the beauty of wood, all the variations of colors unless of course the variation isn't what you looking for.

For those seeking a burl look, stabilized wood is the ticket. You can get it dyed and if properly done it is strong and not brittle. Not all stabilized wood is equal.

I've had good luck with WSSI, he's got the right forumula. I haven't ordered from him in a few years, it's very expensive but it's the ticket for those willing to pay and they'll last forever.