BSavage

This has been an issue since at least 1.16. This bug was reported here - MCPE-152108, but closed as unable to reproduce. 

If you set up a custom mob exactly like tropical fish are set up, only the color2 shows up when you use the tropicalfish material, unless the color that is assigned is 0(white).

All the birds Color2 show, but the only one that shows it's color is the white one in the middle.

If you use the runtime identifier of the tropical fish, the color shows correctly, but you get all the added behaviors of the tropical fish, like the out of water bouncing.

I have attached the addon used for the pictures

As an owner of a large Realm, and a member of a larger Realm community I can confirm that this issue can be almost game breaking for realms. There have already been people banned from realms for exploiting the seed to gain an advantage. If the seed is an easier fix, it would be great if y'all could fix that soon, and get to the rest later. Thanks for looking into this issue. 

I have this same issue and have tried very similar steps. It is also on an iOS device. This issue does not affect my Win10 device. I will check my Switch and see if it effects it, but I think this may be an iOS issue.

This bug effects fishing loot tables as well as chest loot tables. I have made a behavior pack that fixes the loot tables, but it is only a temp solution since behavior packs remove achievements.