Definitely under priced. I have been heard to say on many occasions

that spinners and felters should be willing to pay more than the fiver they were spending on fleece back in the 1970s. What else could you buy for £5 or £6? Not even a couple of glossy magazines

. A fleece is something which will be worked on for months, then used to produce a finished article the maker will be proud of. So you be proud of your product, the raw material for them to demonstrate their skill.
The coloured ones in particular should command at least £10, if they are clean but ideally more. Those spinners knew a bargain when they saw it
Still, as Sally says, maybe by starting them off with a bargain you are establishing a customer base

and learning about marketing at the same time.
Well done for selling them though