If you load a Bedrock 1.7.1 World into 1.8 Bedrock, any pre-existing tropical fish (Previously spawned ones, including ones caught and released with buckets, and nametagged fish) have a chance to change their color palette upon loading the world ontop of the intentional fish resize.

A simple test is to catch some tropical fish in a 1.7.1 Bedrock version of the game with a bucket, release some of them in a contained water source, nametag some of them even if needed, and loadup the world in 1.8 Bedrock. The more you catch in 1.7.1, the more noticable this is due to more fish being present in the contained area. This can potentially ruin fishtank builds for people who caught tropical fish with specific colors.

I had this happen in my Mesa II world. You can download the 1.7.1 variant here (Click Meh!), unzip the files, and put them where they need to be, load it up in 1.7.1, find my lighthouse, go into the lowest basement level and see the aquarium build I have, then load it up in 1.8 to see what I mean.