Watercolor can be applied to paper directly over a sketch, so it's often a good place to start if that's your artistic background. For a bare-minimum investment, you could try this Windsor & Newton set and a pad of watercolor paper.

After that, you can experiment with thicker watercolor paints (like gouache) that will completely cover over your drawing. I recommend gouache tubes rather than jelly gouache sets (which are often deceptively attractive to beginners).

If you want to paint larger paintings on canvas, acrylic paint is more beginner-friendly than oil paint.