I have schluters around niche and windows in 3 bathrooms and they are shinny white and my tiles are matte... I can’t get over how much they stand out and look plastic.

We know a pro painter. Could we paint them?
I would like to know if you guys think it’s a terrible idea or it’s ok?
I would not paint around niche, I found stone instead. But along wall (where tile ends) and around window, I would like to paint schluters (windows are in the shower).

If it’s terrible idea, why is that?

I have an other post but was unable to modify it.