Forgive me for asking but I am TOTALLY lost when it comes to license plates over here. Why does it matter what color your plates are? Why would it fail an MOT if it had black/silver plates? I thought the MOT was meant to check the car to make sure it is safe to drive. What do the color of the plates have anything at all to do with safety? Also, why does the license plate belong to the car and not the owner? How can Brits determine what year a car is based on it's license plate?
I have been horribly confused by all of this since I got here. It sounds so silly to make such a fuss over plates on a car. Personally I am going to run the normal yellow plate on the back of my Mini but I will have a stick on (one of those decals) "plate" on the bonnet of my Mini. I know it must sound sort of "rude" in a way but I have a Pennsylvania drivers license (which is actually expired now!) so if a local cop was to pull me over I really can't see how I'd lose my license. I've been driving for ages now so I'm not too concerned about being pulled over about a license plate's color.....
But anyhow, yeah, why the big deal over the color of the plate? Why does the law care? 
basically the plate belongs to the car so the identity of the car is shown at all times, if the car is sold then the plate (and number) goes with that car.
if the plate belonged to the driver then he/she would be the only person allowed to drive it surely?
we can tell the age of a car by its plate because of what reg mark it carries, so cars made after 2001 will have 2 letters then 01 for the first 6 months and 51 for the second 6 months of the year, (depending when the car was registered), before this however we had a letter instead of numbers for the registration, so yr 2000 was an x reg, on of my cars is an L reg (L194 MNU) you can tell which letter it is as it is the side of the number plate with the numbers. L reg is 93/94
the licence plate is there to show the age of the car and year it was first registered, thus showing the age of the car.
dont quote me on this either but i think the last three letters is a code that shows the location of where the car was registered.
does this help at all?