Red plates are issued to be used before the official number plate is allocated. Often used on new cars, but in my experience very rarely issued by bike sales outlets, even official dealers. I have bought 5 new bikes in my time in Thailand, never had a red plate for any, travelled in many provinces, including Bangkok, and Chiang Mai, and all over Isaan, never had any hassle for lack of plate. I have always carried copy of sales receipt and Insurance which should be issued straight away, never been asked for any of them. Only been asked for driving licence. So whatever the law says, the common practice is to use the bike freely until the proper plate is issued. I guess that would not include crossing any of Thailands borders.
If there are some provinces where there it is a problem, I hope some other posters will contribute to inform you.