Think Value When You Think Color
In this painting, I can see that the artist is trying to make the main object to stand out by using the bright yellow color. However, value contrast is better. We should think about values and value contrast, and use light against to dark to create the attention for the focal point.
The solution for this painting is to paint the area outside of the goldfish with dark blue color. The dark value not only makes the light value of the goldfish to stand out, but also is a complementary color to the orange color to make the watercolor painting look more appealing.