I totally agree I've been looking for the same type of style and when you find one its either on a punk/gothic side or rock style with crazy colors never the urban type feel that rihanna has and i hve looked high and low for styles like what you are looking for alone with the the Rnb singer monica the one where she had one side slightly shaved and come up with nonthing I wish there was a hairstyle creator that would make urban modern styles like that because its missing and in my opinion needed
well anyway I hope you find what you're looking for and by the way heres something its not exact but the texture of it is similar to your pics maybe some way you could modify it
http://paysites.mustbedestroyed.org/booty/ts2/simsconnection/hair/affectionate_object_female/ Good luck =)
edit: the original website is
www.simconnection.com sorry I didn't know i had to give the orginal site adress didn't want to take a chance of hotlinking