The reason I think this may be necessary is that If both Spinals are in instinct and skulls are bouncing off walls and they are both teleporting, Its going to get hella confusing.
Omen has a lighter blue fireball for P2 in the mirror match so why not give Spinal the same treatment?
Also someone in Gutter’s chat suggested that they make Spinal’s skulls purple because of the shadow move changes. I think it would be awsome if they did purple for P1 and blue for P2 or vice versa.
I like the way his skulls are now, but it could be a cool thing if player 2 Spinals, Mirror and others, get a new variation in purple/poison green as the new UI and Logo. Because as you say it would be confusing especially in mirror. But it might be fun too 
But not so good in a competitive balanced manner imo.
Shagos teleport needs this too. Kinda confusing when both players teleport at the same time.
Either way, you’ll both be able to Power Devour them the same. lol
still, if you and your opponent have skulls flying around the screen, it would be good to know which ones you should doge and which ones you don’t need to.
Don’t know if its needed because they will collide with each other and be destroyed.
I think his fireball and soul effects should match his color.
Would be a lot nicer that way