Salmon / trout
I suspect a salmon that hasn't yet been to sea will be pretty much like a trout in all respects, and will not be red. I may be able to confirm this since my local fish market has "baby salmon" right now, which look like oversize trout, but I'll have to figure out if it really is a salmon.
Salmon picks up its unique flavor and red color (which has nothing to do with quality or flavor) by eating crustaceans in the oceans.
The same goes for rainbow trout that choose to become steelhead, they also pick up the red coloring and a different flavor during their saltwater adventure.
Yes, salmon are larger because of their larger environment. Same with steelhead which get much larger than they would have as rainbow trout.
Store bought salmon would not taste the same as the trout of your youth. Farm raised salmon is raised in ocean water (and has the same dye wild salmon collect added to their food for color). Most farm raised salmon is Atlantic salmon even when grown on the Pacific coast because Atlantic salmon tolerate crowding better.
Wild salmon has better flavor and texture than farmed salmon but at several times the price. There isn't nearly enough of it to meet the demand for salmon.
