Yes Nelson must be carrying one dose of the recessive "pink-eyed"
p gene, if he had two he would be a Red Eyed Cream
Nelson has one copy of (or is heterozygous for) a recessive gene which he has inherited from one of his parents. Because the gene is recessive, it needs to be present in the double dose (or homozygous form), in order to reveal itself. He will "carry" the hidden gene, and pink eyed babies will only appear if he is mated to another hamster carrying
p, or to a Cinnamon (
pp) hamster, such as your beautiful Bailey. If Nelson was mated to a non-carrier, then 50% on average (but hamsters like to be contrary) of his resulting offspring will have the
p gene passed on to them, but you won't be able to tell which are carrying the gene and which aren't until the offspring are mated to Cinnamons (
pp) or carriers of the
p gene.
It is a very important gene, responsible for many popular "combined" hamster colours.
http://www.hamsoc.org.uk/varieties.php?id=cinnamon
http://www.geocities.com/dunctonhams/genetics.htm