色白の肌に優しそうな目がほほ笑んでいる。 Her light complexion ?? kind looking eyes were smiling.
Is this に simply 'in'? i.e. "Her kind looking eyes were smiling in her pale skin." That sounds a bit weird.
My other thought was that it might be "due to" i.e. the fact that her skin is pale makes her eyes stand out more.
Two interpretations:
"in"
her eyes are located in the middle of the extent of her light skin
"plus"
she has light skin as well as kind looking eyes
If you take the second interpretation, the sentence becomes grammatically incohesive, but sounds not bad in literary writing.
In fact, I was able to find an example of similar "in her pale skin" in a novel called Kings, Queens, and All Their Things: A Drag Shergi Mystery, so I guess it's not immediately a weird English ... is it?
She had scarlet hair cut around her face then the rest fell down her back. There were brown eyes in her pale skin.
