Does anyone know If we evolve a 14* S-Type pet in the future if they will they keep their coloration? Or will we need to get a hold of a 14* S-Type egg to not loose it?

This screenshot is from the JP version, but it still applies to Global:

As you can see, if the Egg you are using to evolve your Pet is not also S-Type, you lose the S-Type coloration.

It will change into the egg you're using of course. It will stay shiny if you use a shiny egg to evolve it!