Identical twins don't share 100% of their DNA
In identical twins may or may not share identical genetic features, blood type, eye color, height, etc. the rate that twins will share these features in called concordance. Very few features have a 100% concordance, the only one i can find is blood type.
Eye color in identical twins has a 98% concordance meaning that if one twin has green eyes the other twon has a 98% chance of having green eyes. And it also means that on average for every 100 sets of identical twins two of those sets will have twins with different eye colors
Juvenile onset Type 1 diabetes is knowns to be caused by a gene on the 6th chromosome and it has on a 32% concordance. If one twin is a type 1 diabetic the other twin has a 32% chance of also being diabetic.
Multiple sclerosis has a concordance of30%
Left handedness has a concordance of 24%
Rheumatoid arthritis has a concordance of 12%
Homosexuality has a concordance of 54% to 65% depending on the source you refence. It is one of the highest concordance traits we know of
the biggest source for variation among twins actually comes from Epigenetic mechanisms which affect HOW genes are expressed. Epigenetics can act on identical genes in identical twins, say, by switching a gene off in one twin, while it remains on in the other.
This is all basic genetics.