I have edited the Hard mode Completion Marks to match the final bosses:

v1.0:
Mega Satan - Light Red
Ultra Greed - Gold
Hush - Dark Blue

v1.1 adds:
Mom - Pink
Boss Rush - Orange
Mom's Heart - Dark Red
Isaac - White
Satan - Black
Blue Baby - Light Blue
The Lamb - Purple

I was thinking that the Completion Marks needed a spruce up, I feel that each colour resembles each boss perfectly!

INSTALL:
Easy, simply drag the gfx folder into the resources folder.

Cheers,
39Gamer39