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.