I don't have a strong preference as to color, but if I have a favorite, it's red. I generally discourage artificial coloring, but if it looks more or less natural, it's okay. I even like grey or white hair if it's healthy and shiny. I dislike blatantly unnatural color like pink or green.

Nice shine is a plus with any color.

I like straight or wavy.

There's no such thing as too much of it: no such thing as too long; no such thing as too thick.

The more it falls in your eyes, the better. It's best if this happens accidentally, or "accidentally on purpose". Just combing it straight down somehow doesn't do it quite the same for me. I like hair with no bangs, parted way to the side. I like really long side bangs -- mouth length or longer -- parted way to the side. If you can't use both hands and both eyes at the same time, I'll probably like your hair.

I like faux side bangs, held with a bobby pin, that slowly slips down. I like it if your hair falls in your face, and you blow it.

I like it when long hair comes undone. Again, it's more interesting if this happens accidentally or "accidentally on purpose". Just taking it down isn't quite the same. Unsuccessfully trying to keep it from falling down, or feigning trying to keep it from falling down, adds to the effect. If it comes undone because you keep trying to toss it out of your eyes, that's hot.