I'd definitely get someone to check it out, if only for peace of mind. How old is the set?
Regardless, u have ext warranty so common sense would tell me that I needed to at least speak to the source provider, and if still unsure, get them out to check it...call out fee or not.
I have plasma 42 (Pioneer) and don't get any colour flashing such as you report so wouldn't say what ur seeing is normal.
Self help though, is to maybe check scart and other connections before u contact them.