Our threadfin down here look different than the pics in this thread but I tend to work off of hardbaits that work in my area or the customers area.
Here is just one of the 8 varieties I have done....

I use the paint from Spike It (LC gets theirs from Spike It) and just put a dot on with the end of a small paint brush. Not the brush end, the other end. Cut the rounded tip off on the handle end so it is flat and you will get a nice dot maker. You can buy them cheap at craft stores if you dont want to make one though.
If you use the LC or Spike It paint, you are good to go and do not need to dip over it. If you wait to paint for a few days, clean the spot with a little alcohol to get the oils off bait. I paint mine with 48 hours to avoid having to clean.
Jim