Condensed Version: black is a color that isn't supposed to be on any legitimate fish, however due to this glitch, all fish have black pattern color, while most of their base/body colors don't change from their original colors, with a few exceptions, for example, the blue dory and triggerfish.

Pre-existing fish keep their predefined specie names until released and recaught twice, then they give a new name of what color they are now but with the pattern falsely saying white or gray, while only four(triggerfish, clownfish, tomato clown, and red snapper) actually keep their names, all newly spawned tropical fish that spawn(except the four species previously listed, and blue dory fish, as those automatically turn into triggerfish for some reason) from the reefs, or creative mode buckets/spawn eggs already have glitched names and pattern colors.

Pre-existing Anemone and Red Lipped Blenny fish in buckets have the name, "Bucket of item.tropicalSchoolAnenome.name" and "Bucket of item.tropicalSchoolRedLippedBenny.name" however when spawning the fish, they get black pattern colors, and altered names of their new stripey and snooper colors, also with incorrect pattern color description in the name.

These fish don't fix their textures whenever I turn my console completely off and unplug it, and then reconnect.  

Extra Information and how I discovered this glitch:

So once I updated to 1.8.0, and got on my Survival world, my fish tank of blue tangs(blue dory) turned into triggerfish.

Along with that, I looked at my pond of tropical fish, all of their pattern colors are black, however most of their body colors, and all of their 3D models stayed the same, except bigger(the size thing was intended, but not the rest).

Also when you first catch them with a bucket, it'll say what the fish's original predefined species, or color pattern was (for example, previously owning a orange-sky stripey, then updating to have it become a white-gray stripey, when caught will still say orange-sky stripey), until released, and then it says what it is now with this update once caught again.

After this, I went to the closest reef to re-stock on fish to find out that all existing, and newly spawning tropical fish in that reef were also affected, and none of them had any other pattern color other than black, and all predefined species such as clownfish, blue dory, moorish idol, parrotfish, etc. got their body colors completely different colors than they're supposed to have.

Currently I'm now in a creative mode world, and all Tropical fish from the buckets and spawn eggs are also suffering from this problem too.

I'll make an Update to this report once I find out what all predefined species of the fish are completely messed up, and which might be unaffected, as I do have a creative world with all of them in buckets.

Update:

Seems like every prefined specie of fish is messed up in one of two ways:

Name in bucket:

all of them except the triggerfish (which also has a gray body color now instead of the usual white body color), clownfish, tomato clown, and red snapper (these three keep their names and their body color, but their pattern color is black), have their bucket name turned into a color pattern name of their fish model however, with of them saying their pattern color is white or gray despite it obviously being black.

A blue dory fish placed or spawned in the world turn into a glitched color triggerfish, however a triggerfish stays a triggerfish but with a glitched color, confirming that triggerfish and blue dory fish are not swapped, but instead are just the triggerfish now.

Then there's two fish, the Anemone and Red-lipped Blenny fish that have a glitched debug name as their bucket, "Bucket of item.tropicalSchoolAnenome.name" and "Bucket of item.tropicalSchoolRedLippedBenny.name", which when placed like expected are also glitched, and will most likely will change their name to the new Stripey and Snooper fish they are now once recaught and released two times.

Also even fish with naturally gray patterns such as cichlids, moorish idols, butterfly fish and such don't keep their name either.

Fish Color:

All the prefined and custom mutation tropical fish species now have black patterns, but somes predefined fish keep their body colors while having their pattern color become black, (for example clownfish, red cichlid, red snapper, and emperor red snapper).

Others who have natural gray patterns seem to keep their body colors, but their patterns are black, so by appearances (with the exception of the triggerfish, and blue dory fish which have the problems previously mentioned), they are also effected, and their bucket names are messed with to say the type of fish 3D model they are(for example cichlid, butterfly fish, and moorish idol).

However, the only predefined fish specie with their body color being incorrect is the blue dory fish and triggerfish, both having a gray body color rather than a white(triggerfish) or a sky(blue dory) body color, all others keep at least their body color.