As per my pp, many people want darker skin, they tan, they use sunbeds and they use fake tan. All to look darker. I suspect Sam was trying to make the red head feel better because she had 'pale' skin unlike her sister who had the beautiful darker skin. That's not to say my opinion is that pale skin isn't beautiful too, I'm just saying a lot of people (women especially) always seem to want darker skin.
I don't for 1 minute believe it's a case of 'casual racism'. MPO is that sometimes people want to start drama over nothing.