After doing a lot of work and testing on a skin of mine, I managed to break it somehow.
When I now try to load it, I get:
"Unable to load element: 1506082618 - Value of '524' is not valid for 'green'."
But searching for '524' gives no results.
(of course I might have mis-typed that once, but it's not in the skin file now)
I must have made some typo, or copy/paste error somewhere, but I cannot find what it is and fix it.
Does this 'element 1506082618' give a clue where I should look?
After closing that error message, I get this panel: