A triadic colour scheme is used in this illustration, the colours blue, purple and orange that are evenly spaced around the colour wheel. Triadic colour harmonies tend to be quite vibrant, even if you use pale or unsaturated versions of your hues.
Saw these style boards on Oriental Trading for use as geometry boards. Wondered a diy hack. Use glue on bottom circle of thumbtack to secure it from being plucked out by little fingers. Sowdering About in Seattle: Toddler Busy Boxes