Rj568a vs rj568b?

It's true that electricity doesn't care what color the insulation is. What the standards do is assign meaning to the colors and the pins on the interface. In a simpler world they'd just be using the USOC standard designed for voice phones: pair 1 in the middle, pair 2, 3 and 4 spreading out from there. AT&T modified that so that the outer pairs weren't split so far apart in the connector, minimizing the chance for crosstalk, and that's probably why pairs 1 and 2 aren't so close together.

Then comes the rest of the communications industry, who wanted a standard not controlled by AT&T. In comes the EIA/TIA 568 standard... based on what AT&T was doing. The main difference is that pairs 1 and 2 are together so that they are backwards compatible with voice wiring. With the AT&T pattern so widespread they grandfathered it in as 568B. And the rest is history. 568A is preferred and what you must use in government contracts.

Using the twisted pairs as pairs is essential; each pair functions as a "transmission line", a bit like a coaxial cable but balanced rather than one half grounded.

As with coax, a properly made pair has a constant impedance and very low signal loss over long distances. Random wires just do not work the same.

Other than that, the only thing that matters for it to work is having the same pair on the correct terminals at the other end.

Using a particular colour code just makes it easier to faultfind or reconnect thing is future, as you can look up what colours should go to what pins.

The specific colour arrangements are for compatibility with other or older systems, if the wiring is eg. in an office building and may be used for phone or other purposes.

Logistics in other words, not any technical functionality.

In real work ,the most used standard is rj568b that not only refers to crystal UTP crimping .

1. Devices know the difference because you will essentially be connecting some wires to the wrong place if you mix and match. Mixing them will essentially create a long crossover cable, and you may have trouble establishing Gigabit or higher speeds. You especially don't want to mess it up if you'll be using Power over Ethernet (PoE). 

2. The plastic is not what is changing. It's the order of the wires in the plug. 

3. If you are connecting two devices together with no other splices or cables in between, such as a computer to a router, the pinout standard truly doesn't matter. Where it does matter is if you're connecting it to another cable, such as a jack in a wall. You want to use the same connector wiring standard for both your patch cable and the in-wall cable.

Look, if you're really confused by this, just think of it like putting batteries in backwards. 

There is a slight difference.   Look at the Twist Ratios of the Wires.