In fact A and B colour coding wiring schemes are both equally valid. The important things are to use the SAME standard at both ends of the cable and especially to keep each of the pairs of colour matched wires twisted up to the point where they are connected. A simple cable tester tests DC continuity but not that the wire pairs are correctly matched (e,g Orange+White stripe must pair with White+Orange stripe etc. If they are not matched the cable will not work.B is crossover which is for network wiring..
A is straight through for device to device communication e.g: pc to pc
If you wire to the A standard at one end and B standard at then other end you have a "cross over" cable. Just to add to the fun - many computer devices (especially network switches) can detect a crossover cable and compensate for it.
There is no distinction between data and any other use for Cat5/Cat 6 cables. Telephone wiring is less critical and uses different colours (but can be passed over CAT5/6 cabling)
[I am a (retired) computer network designer]