There are two standards that are generally followed for cabling color coding and routing standards: TIA 568 series and ISO 11801 series. Technically speaking, if you have continuity, you can use whatever colors you want. Realistically, you will get old and gray early trying to keep up with what is what and what pair goes in what position at each end of the cable. Add crossover cables to this mix and it becomes even more complicated. So yes, technically you can, but why would you?