When I catch a tropical fish and it shows me the type (love this new feature) and bring it back to my house that is about 100 to 200 blocks away, it turns to a white looking fish instead of the original color I caught it as. Now, I'm not sure if this is a feature made to resemble real fish where in real life, they will turn white (not sure if that's a real thing). But I also tried replacing the caught fish without leaving the ocean and the tropical fish still turns white. The fish types I've seen them turn into is Bucket of White Blockfish, Bucket of White Spotty, Bucket of White SunStreak, Bucket of White Clayfish, and a Bucket of White Betty. I've also noticed that if a tropical fish ends with it being a Blockfish, then it will be a White Blockfish after being picked up with a bucket. I hope you can find this explanation useful.