It could be a German Red, as a hybrid /line bred fish there will be a lot of variation colorwise as adults.
It's Aulonocara sp. "Stuartgranti Chipoka". Unless it was crossed with another species of peacock, it's not technically a hybrid.
Does that mean it's not a "German Red"? Nope.
Does it mean it's a "Red Rubin"? Maybe.
Could it be a "Rubescens"? Perhaps.
Those three are all line bred from the first one I listed. The color ranges from yellow to red. My understanding is that the "German Red" is line bred for the darker portion of the spectrum (more red), where as the other two are somewhere on the middle-lower portion of the spectrum.
While you would expect with good line breeding practices all the fry produced would look like their parents before being sold as such, from time to time culling a few outliers is probably necessary. If not, the line breeding efforts could be diluted. Many people aren't particular enough to care, so dilution isn't unlikely at some point.
My concluding thoughts.... It's not what I would call a "German Red", or a "Red Rubin" based on those I've seen/kept. I would consider it a "Rubescens" before the other two. Would I fault the supplier you got it from? No. Would I get stock from somewhere else if you really want a nice "German Red"? Yes.
As for the coloration vs size with regards to specifically "Haps" and "Peacocks": Some fish just color up better than others. I believe some of it's genetic, while some of it's environmental. And with regards to the environmental portion, I think there's a critical period before it's full grown in length where if it's stressed (aggression from other fish, poor water conditions, etc) and doesn't color up well, it'll never reach the potential of the species.
