depends. anything that's rarity becomes nice. back then dark hair tops were popular and hence sasunaru was popular and now a days blonde seme are in so narusasu is popular;)
I don't think so. It's more about the preference of what the readers like. Black-haired tops are a classic from way back, because blonde hair is usually used to describe a Yankee in old manga, or like a thug. black hair was used to give a mafia, or proper businessman look. But in the end, their attractiveness depends on how the artist portrays them.
I am more of a light-haired Seme person, though.
Personally, I think preference and what you associate with those colors help to decide which you like more. Black hair is classic, since most people have dark/black hair. Blonde or light hair is more new, in the sense it was not as common until now. Plus, blonde can be used for the westernized “popular jock/jerk” trope, or golden retrievers. Black hair can be seen as feline, or cold. ╮(￣▽￣)╭
But, if you were to roughly generalise...would you say dark hair tops are more attractive than light hair tops?
I was just thinking about it, and I couldn't reach a conclusion.