The real red looking RT's you're talking about are considered SRT's. Most ppl label regular RT's as SRT's. The SRT's are selectively bred to probably all red flowerhorns to get that true red color. I'm sure it was a while before they got them consistent. I honestly don't think it's just from a fading fish, but it could be. i added a pic to show how flowerhorns pick up the red even in faders. Just my 2 cents.
Here;s some photos for reference. This is your classic SRT. Look how sunken the eyes are. Definitely bred with vieja or flowerhorn that was already cross with vieja.
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Here you can see how a faded flowerhorn can possess a true red. Maybe not the entire body, but I'm sure down the line after much breeding, they got them to come out all red.
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They say this is a SRT because it's probably bred with flowerhorn x red texas. YOu can clearly see this looks like a kamfa
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Hey, I thank you for your 2 cents! Ok the red mammon and flowerhorn texas crosses I am very unfamiliar with so I can't elaborate on them. I should have been more specific in the title to only show bp/tex crosses that have went through a fading process and still display a deep red color. But I would like to know if the first one you showed(mammon cross) went through a fading process? Also the last pic shows signs of fading because of the black morphing color on the fins... I'm sure that took years of line breeding and that was still a 1 of a kind fish out of a 100+ grown out. Let get more fish showed from people who know more of their fishes background.