Role playing sexy chatroom
If you can't find what you're looking for, you can create a free forum at Invision Free, Pro Boards, or Zeta Boards.
Roles can be general designations of power positions, or very specific, detailed fantasies.
The default palette isn't too great, but it can very easily be augmented and/or replaced.
I've got a collection of colors that look pretty decent in Chatzy here.
A free and easy-to-use chat service that works on desktop and phone, with or without registration. You can even find RP bots to add to your server over here!
Charat is a "pan-fandom" chat service not dissimilar from Omegle where people interested in roleplaying can potentially be found.
How seriously the play is taken depends on the people involved, and the scenario may be anywhere from simple and makeshift to detailed and elaborate, complete with costumes and a script.