I first used a non-stainable PC-Woody to repair some cracks and nail holes on treated deck posts and railings without thinking. When I realized my mistake, I switched to a stainable wood filler (DAP plastic Wood-X). I thought I was doing the smarter thing :) Guess what! It turned out to be that both are not stainable. They look lighter color than wood itself after stained. I am painting my deck railings and posts, with Behr Semi-Transparent Waterproofing Exterior Wood Stain and Sealer (California Rustic color). Is there a way I can remedy this? I am wondering if I sand the wood filler, can I apply some primer on it and then use the stain again or some other way.