just using regular acrylic paints. using a brush with VERY little paint on the brush, lightly brush leaving just the hint of color. that is called dry brushing. I will usually brush on a piece of white paper to wipe a lot of the paint from the brush until it is leaving just a hint of color before applying the color to the bait. repeated brush strokes will allow you to build the color.
when I do the back and belly of a bait I use rattle cans a lot and just mist the paint on. make a hanger from a paper clip and hang the bait from the line tie. then hold the bait at arms length and LIGHTLY spray. just short bursts so you can see the coverage. takes some practice but not difficult.
now consider that a clear coat will make the details, in this case the scale pattern, stand out. in the picture I posted the scale pattern was to me too stark. I should have used a pearl white over it prior to doing the rest of the paint detailing. the pearl white lightly brushed on will soften the dark lines of the scale pattern without totally covering it.
remember that with brushes, easy does it. you can add paint, harder to take it off !