Well I'm not sure about what colors would turn someone on. I guess it depends on there phsyche. For me any color will do, after all I'm just happy to see the panties!
I once dated a girl that had these panties with a pink heart on the front and two on the back on her butt cheeks. God I loved those, wish I had stolen them after we broke up lol.
Eh, depends really when/how they are worn :P
Like say with a T-shirt/tank top (Y'know .. "casual" at home wear) is awesome to say the least.
Personally I put preference on Blue, Green, Purple, or coloration/hue of said colors.