Encourages visual memory, copying, direction planning and movement. Can grade the activity by only having the colors needed or having the child pick the colors out of a bin of numerous legos of different, shapes, sizes and colors.
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