You can download these Rainbow Shape Printables here — shapes
Laminate the cards and then have the kids use a whiteboard marker to draw on them.
First Sage used the Printables to select the correct shapes on each card with a tick and the incorrect shape with a cross.
She then sorted the Rainbow Blocks (From Sweet Elephants) into the correct shape. We placed each description card on a mirror (I bought them in a clearance sale from Modern Teaching Aids) and she set the shapes out on each one.