Well, start by understanding the mood and tone of the scene. Choose colors that match that. Also, pay attention to light and shadow for a more realistic effect.
The key to coloring manga panels is practice. Experiment with different color combinations. Study how professional artists do it. Also, use the right tools and materials to get the best results.
To color manga panels well, you need to have a good sense of color theory. Consider the character's emotions and the setting. Use different shading techniques to add depth. And don't forget to blend colors smoothly for a seamless look.