Almost any kind of paint will work. We've used wall paint, acrylic craft paint, chalk paint, and chalkboard paint with great results. We recommend using a bristle brush, foam brush, or a small foam roller (depending on your preference), but would not suggest spray paint as the overspray could make a mess (we've tried!). If you have a particular project in mind, we'd be happy to send samples you can test to be sure the stencil decal turns out just the way you've planned.
For most projects, we recommend first painting a thin layer of paint in the SAME color as your project surface after the stencil is applied to eliminate any bleeding. Allow that to dry (usually 1-2 hours is sufficient) and then apply the paint in the color you want for the design. Then we suggest waiting another 1-2 hours for that paint to set before removing the vinyl background. You have less chance of smudging your design that way.