Bell and Tremper are not line bred, they are simple recessive. There is no way to know by looking whether the gecko has a gene for Tremper or Bell. You could test breed it to a Bell or a Tremper, though if you're wrong, you'll have geckos with albino genes that are even more unknown. Many people will say that is you have no way to find out from whoever bred it which strain of albino it is, it's best not to breed it.