When you say sample, do you mean a sample you made up, or one in the store?
I bought a can a couple years ago and thought the effect was so bad I have
never used it; on maple and poplar it looks more soiled than walnut. Maybe
it works better on oak.
If you are going by the store's sample, make one on the wood you will be
using before going too far.

I have used Behlen's waterbased filler. That goes on before staining. It
would make an awful mess afterwards.