Actually, the mice work best when they are pale and rubbery. I have no idea why, but it was recommended to try on non-feeders, I did it and found just dipping the pinkies in the boiling water quickly doesn't do the trick. Leave them to cook a little and the hatchlings went wild for them.
Easy to do and it saved at least 20 of my hatchlings this year from becoming cobra food.
I do the same thing and have gotten several non-feeders and some very picky eaters to eat. Usually, after eating a few like this, they will go on to reguler thawed pinkies.