[?] Question about twins

My Sims have a twin (a boy & a girl). Totally different in terms of features & the eye colour, but both of them have the same hair colour & skin tones.

The sims in my profile picture are twins. So they have the same eye color, but different hair color and facial features.
But I have also had multiples that look very much alike, so I guess it depends. :)

They can be identical or fraternal. One of my current households has a pair of identical twin girls. I was really glad they turned out to be identical, since their names (Demeter and Ceres) were taken from the Greek and Roman names for the same goddess.

I find that identical twins, just like in real life, are much harder to get than fraternal twins.