Rather than remove the original skin, which admittedly would have been easy enough to do, I elected to build more fish skeletons so that I can display the skins together.
See both koi and the shark side-by-side after the break...
I'm no koi or fish expert but a quick Google would suggest that this is an entirely fictional colour scheme. Nevertheless, it looks excellent.
The left side is primarily pink; the left more greeny-bluey. Both are very attractive.
As I said in my review of 81000 Koi there are no rare parts in the set, other than the new pin to hold the skin in place, so if you have a reasonable collection of Technic pieces already you should be able to build copies of the skeleton easily enough.
I built two, together with rudimentary stands, so that I can display three together. (I have no plans to colour-in the fourth skin).
Without doubt this colourful creature is my favourite of the three.
I hope you've enjoyed our LEGO Forma reviews and, if you ordered one, enjoy building it as much as I have.