I have never tried any commercial stain sticks on a blemished stitch but maybe other stitchers here have, so we'll see what the other stitchers have to say about doing this. I have read that you could try a little lemon juice on a Q-Tip and apply it just to the blemished stitch to see if it pulls out the stain since it is white and lemon juice has a bleaching effect, but sometimes the discoloration is in the thread itself (I have not seen this discoloration happen in the thread but once in a great while if you use DMC floss) where it may not have taken dye so if that is the case, it is not likely that anything will change the color of the dye-less thread.