Easy to bypass these services with a paperclip to give 5 greens. So I'd look more for genuine paperwork more than the lights.
The 5 green lights 'would' mean that it's been recently serviced, so owner should be able to show the receipt. No receipt, no service.
Can buy a service reset tool for £10, so until said car is under your ownership, dem lights - mean nuffink without paperwork.
Orange, and red have different service intervals, but unless you have FSH - doesn't mean much at 20 years old, easy to bypass and put 5 green lights on the dash.
Look for one here, in the FS section. And look at the buyers guide as to what to look for under resources.
Welcome to the forum and do feel free to ask us members our opinion on possible purchases. But get one from a forum member, there are other forums too. This forum, very honest, with zed sheds willing to do major as well as minor work. If you want to be handy with spanners, plenny o guides and help.
Best of luck
