Some of the shiny Pokémon in Colosseum are colored a little differently then they were in Ruby/Sapphire. A lot of the sprites on Fire Red/Leaf Green are a little bit different then the sprites on Ruby/Sapphire, at least as far as their poses. Their coloring stays pretty consistent from Ruby/Sapphire to Fire Red/Leaf Green. I am not 100% sure, but I think that the shinies in Fire Red/Leaf Green will be pretty much the same color as they were in Ruby/Sapphire.