I've been doing a lot more 3 star battles lately. I noticed like every single one of them is Whitehelm and keep getting yellow arcanes. Therefore any arcane I have more then anything is Yellow
My suggestion is,
If I fight Whitehelm or any kingdom make the arcane drop completely random. Just like if you do a treasure hunt, you have no clue what your gonna get. If I really wanted to get a certain arcane, I would go explore. This will help save explore time. Keep the same drop rate in PVP but make the arcane drop random.
This should help keep the colors more even. Beside would be more interesting when you do a PVP match don't know what your gonna get
This is my personal opinion but I figured I would share it