This has happened to me numerous times now since the last update back in May.
I will be working on a drawing and working with different functions including editing "named colors". No problem. THEN, all of a sudden, I'll go to edit a "named color" by clicking on the color I want to edit in the "Color Gallery", and all the options become grayed out with the exception of the "New" option.
It doesn't happen consistently, but when it does, I have to close Xara Pro 15.1 and restart it to get the functions back.