Writing other color spaces than RGB in hex

I'm working on an iphone application that is going to feature a custom color selection tool. The application supports various color spaces and I'd like to use hex because the codes are shorter and more convient to type on an iphone.

So here's the problem: I know a 6 digit hex code can be used to store any sequence of 3 integers in the 0-255, but should it be used for that?

I've never seen hex used for anything but RGB and I'd like to know if I'd be infringing some unspoken rule if I used it for HSV, HSL, and YIQ.

I do not want to mess with conventions or standards but I also want a convienient text representation that's suitable for a user-base of designers and artists.

Thanks in advance!