How are straight and crossable cables different from each other?

We use straight cable to connect two different layer devices like router-pc, router switch as well as the switch pc while the cross cable is used for connecting two same layer devices like a switch with a switch, a router with router and pc with pc. Color-coding for both the cables is different. However, if the color-coding on the end of the cable is same, then it is a straight cable. Whereas, if 2<->6, 1<-> three is used then it is a cross cable used for data transfer.