From The Fishery Biology of Sea Urchins in the Family Strongylocentrotidae, Washington Department of Fisheries, 1976

If you cut the sea urchin along the equator you will see the following:

Am and Im are the ambulacral and interambulacral areas respectively.

A is the "top" and B is the bottom or mouth side.

Gonads are usually yellow to orange in color [about the same color as the eggs]

Stomach and Intestines are usually olive drab to brown in color.