Colour of magic and light fantastic are 2 of the worst books in the discworld series. They’re not bad books, but nothing compared to what comes later. I read the series in chronological order and don’t regret it, so don’t give up on it. You can also follow the story arcs, if one particularly appeals to you.
Witches is a significant step up, and it only gets better from there, as Pratchett hits his stride.
I disagree, they set the scene for what’s to come.
We see ankh morpork and the wider discworld through the eyes of rincewind (lives it, knows it, mostly hates and/or scared of it) and twoflower (all new, loves it all, naive).
So it sets the stage for all the other characters to enter and exit from there onwards.
Don’t get me wrong, they are important books, and quite good. They just lack something compared to the later books. It’s like the shutter start effect on some films. Initially it’s a bunch of stills. At a critical point it becomes a stuttering moving image. It finally becomes a living breathing film.