Colors are important to make your presentations look good, but not everyone has a good sense of which one will complement another. Zach Holman suggests a cheat: go to a site like ColourLovers and look through palettes suggested by designers.

The "Most Loved" section is a good place to start, but you can try some of the other categories too and find something you like. But you still need to be aware of where it's going to show: a projector.

Usually I look for bright colors that go well on projectors. That means colors with a lot of contrast. For example, choose a dark, a light, and an accent. That way you can layer the dark on the light and still read it from in the way back of the room you're giving the talk.

Holman also suggests breaking up different sections in different colors. There's plenty more advice in the link below, including how to get those colors into your Keynote.

Color | Speaking.io