Hello! I updated the redhat-artwork package to a more recent version and added support for building without the GTK1 Bluecurve theme, so you can build this on systems that have only GTK2 installed. It's just a simple hack like the KDE checking in this ebuild, and I've only tested it on systems with no GTK1 installed. It checks for the "gtk" USE flag, and if no such one exists, it disables the building of the GTK1 Bluecurve theme.
Created attachment 4625 [details] redhat-artwork-0.47.ebuild
Oh, and modify or remove my comment about the gtk1 disabling and anything else freely.
Fixed this awhile ago and forgot to close bug apparently. Thanks.