LoL, but isn't Forte as a character just a angry slightly edited Rock?
What makes you think that? Forte's design is more comparable to RockmanX's than Rock. He's quite a bit taller and has both a chest armor and bulky shoulder pads.
I mean, nobody was ever complainting about Blues, who is also a edited sprite of Rock.
That's absolutely not the case. No matter how much Blues resembles Rock in terms of design, his sprite is completely unique. The body posing and proportions are different.
Compare that to R10's Forte, and it becomes obvious that for all Forte's many actual differences with Rock, his sprite is closer to Rock's than Blues' is. Which is just plain bad.
Although, I still wish they used a darker shade of gray
The NES palette doesn't have a darker shade of gray than that. Which is why a character such as Reggae was drawn completely black. However, Forte being a player character has to exist on black backgrounds also, presenting a very tough dilemma. A dilemma to which I've been pondering the answer myself; the gray is just too light, but the all black presents some gameplay issues.