As stated in the title, it is currently not possible to have a color gradient on a 30 series Strix GPU RGB, while having the GPU synced with Armory Crate Aura Sync. When it is synced with the rest of your system the whole light bar of the 3xxx series Strix cards are one solid color (color cycle). The only way to get the GPU LEDs all not one solid color is to un-sync from the rest of the system, and let it go rainbow mode on its own, and there is no other color gradient option. Everything else is just color cycle and all GPU LEDs the SAME color at once.
Chances are you paid big money to get your hands on a 30 series GPU in todays market, and even more money to get a shiny Strix version, only to find that the software is not working as advertised.