Light and Dark Eyes

Two girls, one slightly older than the other one. The girls are so similar in their appearance that they are likely sisters. Their noses and lips are nearly identical, as is the shape of their faces – even their dresses and their hairstyles match. There is one striking difference, however: the older girl has very dark eyes, but her little sister’s eyes are extremely light in color.
The photograph has been taken at the photography studio of Sv. Svensson in Linköping, Sweden, at some point during the early 20th century; I’m guessing the 1920’s.