It depends largely on a variety of factors. Twins are when two children are born from a single birthing to the same mother. Most people when they think of twins think of identical twins
who are - in effect - copies of one another since they have the same genetic blueprint and are the result of a single fertilized egg that splits into two individuals.
Yet, there are twins that are the result of the fertilization of two eggs at practically the same time and each egg grows into its own baby. These twins are known as fraternal, and can
have very different genetic make-ups because they are formed from separate sperm and egg combinations.
In identical twins, there can be minor differences in the appearance of the individuals, but these aren’t commonly very pronounced differences. Perhaps one twin will have a mole that the
other doesn’t. Yet, different haircolor is very rare for identical twins as far as the hair color with which they were born.
Of course, environment can have an effect on the look of the hair. If one twin spends more time outdoors in the sun, the hair can become lighter than that of his or her counterpart.
With fraternal twins, the haircolor can be wildly different since the genetic mapping for one twin doesn’t necessarily match that of the other twin. Of course, if a certain haircolor is
dominant in a family, it would be common to see the twins with the same haircolor, regardless of other differences. But having a similar haircolor for a fraternal twin is no more likely that for any other type of sibling relationship.
So, you have your full answer to the question, but you can boil it all down to say that “Yes, twins can have different hair colors.”