Custom colors do not persist across sessions

[phchang]

When I create a custom color in the "Edit Colors" dialog, it does not persist across sessions (e.g. refresh the browser).

I don't recall actual behavior in Windows 98, so I'm not entirely sure this is a bug. The linked emulator in CONTRIBUTING.md also does not persist colors if you close and reopen MS Paint.

Either way, it would be nice if the colors did persist — it would keep with the aesthetics of the original and be a nice enhancement.