If necessary, darken the areas around the white spots.
I used too much water to start with, so I had to paint them a couple of times.
Controlling the amount of water is one of the most important aspects of how to paint watercolor.
Adjust the shape of the white spots where needed.
Now turn your attention to the butterfly's body.
Paint the left, shadow side dark. Lighten the value toward the light and leave a few highlight for interest.