If Magma Man's sprite is not possible, Eddie or the head of the fire dragon sub-boss would help as they use the same red. I don't checked Rush yet, but I guess he uses the same color too.
Another sprite that could help is Tornado Man as he has two new colors (different green and orange). I believe one of the green colors in the Hornet Man stage image is this one, but stage colors are more complicated to check then cutscene and sprite colors... But it still would be useful because of the orange. If not possible, orange can be obtained in any sprite of Mega Man, Plug Man or Splash Woman, and green can be obtained with the green cannons or the plant enemy in Concrete Man's stage.