Blue or purple. Basically anything not pink, but that's unavoidable at times as some toys that have a great design appear only in pink. If I can avoid it I skip pink though.
In order of preference... black, stainless steel, blue, red. I'm guessing those colors are mostly a guy thing. A hot pink or lavender toy would be a turn off for me.
I don't have a preference, I just buy what is right for me. My first toy was orange. My other toys are blue, pink, black and purple. My boyfriend likes seeing the black against my super pale skin though.