I'm actually more surprised 200k people have downloaded a custom colour scheme. But since they have, I don't think 10 EUR is excessive to charge for something like that.
Its value is in the fact that it's free.
I can see buying _icons_ being a bit more justified, because it implies at least some amount of non-trivial work on your end, but I don't really know anyone willing to pay for better code editor icons.
Also the fact that you offering to buy a "license" is off-putting, again considering the context of selling a set of RGB values. It's too grandiose, which too contributes to this looking nuts. Just say "buy" the scheme and it'll already be much better.
I totally understand that someone would charge money for it.
I think it depends on what you think is trivial and what is not. I think designing a coherent theme is not trivial.