Not exactly a true statement. Amphilophus can have many colormorphs. There are even some that are refered as "Piebalds" because they only partially go through the colormorph of barred to colored.
Depends on the fish. I probly have the most layed back Midas on MFK to date. He currently resides in a 125g with Platties, Clown loaches, neon Tetras, Albino Plecos, and Bettas. Not to mention the tank is fully planted. Latest Video is in my avatar.
Unfortunantly Petsmart doesn't sell pure Midas or Red Devils. Their a mix and just labeled as what they suspect will sell best in the region. I worked there almost a decade ago, so trust me on that one.
a 300g will be fine for all thats for sure. 90g will be fine for about 6 Months, maybe less. Again, it all depends on the fish. Mine is the exception to the rule. 99.999% of the time a Midas would destroy the setup I have. This one just happened to be that .001% and my experiance with Amphilophus allowed me to recognize that. Now I stick my hand in there it is another story.
Anyway, welcome to the Amphilophus Addiction. Weather it is a hybrid or pure, you can't go wrong with them.