While driving around BKK I noticed few registration plates that are different from usually used in Thai. First one was red colored plate that started with English J and some 4 digits, it looked like an "temporary" one. The second one is light blue color with some letters that looks like Thai and 4 digits, is it Cambodian one? Thanks for clarifications guys.

Red is new car. Blue is usually diplomatic.

Red is new car. Blue is usually diplomatic.

You not reading my original post. It say red plate with English letter in the beginning. Diplomatic numbers wont use Thai or cambodian letters as well in their numbers, right?

Sorry no idea then

OK, I saw one of the red 'J' plates today, I am 99% certain it is a conventional dealer plate.

Blue plates with white lettering are embassy vehicles (not diplomats) which have been imported at a reduced duty level (or duty free?). These cars cannot be sold for (I think) five years.

Also yellow background = vehicles for hire like taxis and motorcycle taxis.