Online Tools for Choosing Colors
When I pick a mandala coloring page, sometimes I know exactly what kind of color scheme I want to use. Other times, I've got no clue.
I use two methods for picking colors. First, I "wing it", picking colors as I go, using whatever color I think fits best. The second method is to have a basic idea of whether I want it to simple or complex colors - two colors or more? Most of my coloring is done with three to five colors, but obviously this is art and you can do whatever you want.
I found an Adobe tool online for picking colors, and I've actually used it for non-coloring activities (like working on websites). Another, somewhat outdated but still useful, tool is from Visibone's Color Lab. It has been around for many Internet years.
Typically I'll chose whether to go with a monochromatic look, a rainbow effect, or color-blocking. Those are my favorites. I don't typically use shading or gradients unless I'm using colored pencils.