Toriyama's editor was initially against having Goku grow up, saying it was uncommon to have the protagonist drastically change in manga, however, he gave in when Toriyama threatened that he would not be able to continue the series if the character did not. Toriyama later stated he had him grow up as a means to make drawing the fight scenes easier. When Toriyama thought up the Super Saiyan concept during the Freeza arc, he felt the only way to show Goku's massive power-up was to have him transform. Initially he was concerned that the facial expression looked like that of a villain, but felt it was acceptable since the transformation was brought about by anger. The Super Saiyan form also spared the trouble of coloring Goku's hair all the time for the standard black-and-white manga pages. This was the reason for the Super Saiyan form having blonde hair, because it was easier to draw for Toriyama's assistant who spent a lot of time blacking in Goku's hair. Goku's piercing eyes in Super Saiyan form was also inspired by Bruce Lee's paralyzing glare.