In relation to Goku, Toriyama says on Goku he made his hair blue to express how "by overcoming a certain limit he has become both strong and tranquil, able to keep his composure in a fight".
It's assumed to be coloured blue as the hair is also blue in the few coloured manga/illustrated materials depicting the form.
The reason is the crown that Paragus (his father) has created restrains him from transforming into his regular SSJ form.
Super Saiyan God is the least dramatic Saiyan transformation. Visually, the Saiyan bears no distinction from their base state save for three features: their muscle mass shrinks down, making it look as though they have lost weight, their hair becomes wine red, and their eyes become bright red as well.
When Saiyans become Super Saiyans, why do they get blonde hair and blue eyes? Because Toriyama apparently wanted to give his assistant a break where he would no longer have to ink in Goku's hair and save time due to that.
The original Broly was able to only power up so far before the Mind control crown that Paragus placed on his head began to kick in and suppress his power, not allowing for him to go any further. His body would be enveloped in a pale green aura and his hair would turn blue-ish or purple.
He is Bulma's son so he would have the same hair as she does, which in the manga is blue but in the anime is purple. Toriyama redesigned trunks for dragon ball super and of course, directed the studio to make him with blue hair. His younger self stayed with the purple hair as an inside joke.
Because Black was a fully divine being, his transformation was pink instead of blue. The Super Saiyan Rosé form allowed Black to easily defeat a Super Saiyan Blue Vegeta and fend off a similarly transformed Gokū.
Previously, Kotaku reported that leaks could indicate a pink-hair Super Saiyan was a thing. Now, we can confirm that for sure. Meet Super Saiyan Rose.
This is the newest and most powerful form a Saiyan has ever been shown to achieve and is a fitting way to close out the Dragon Ball Super series. In this form, Goku's hair and eyes are completely grey. His power is level gains a huge boost, though it is extremely damaging to his body.
In the initial promo for Broly - The Legendary Super Saiyan, Broly was shown to have gold hair in his Legendary Super Saiyan form immediately upon transforming, but in the final release, his hair is colored lime green and doesn't become golden until late in the movie, and also remained gold in the sequels.
Super Broly (超ブロリー, Chō Burorī) is the name given to Broly's unique Super Saiyan transformation.
The Saiyan Beyond God state isn't necessarily a transformation. It is simply the name applied to the state in which a Saiyan has mastered the Super Saiyan God transformation, to the point where they are able to utilize its divine power without transforming into it.
So while Super Saiyan Blue is stronger than Super Saiyan god from the first arc, Super Saiyan god has more potential. It has been said that a user of the form god-like saiyan, if they go Super Saiyan while using the technique, the automatically ascend to Super Saiyan Blue.
Toriyama “wanted to eliminate the time spent coloring in black [hair]” so he simply left Goku's Super Saiyan hair uncolored in that original reveal to save himself some time. “For a serialization that's published weekly, each minute and every second is precious,” Nakano said.
The reason Super Saiyan is SSJ is because the actual Japanese term is “Super Saiyajin.” This is why many fans add the J, to symbolize that very fact. Saiyajin is literally Japanese for “People of the Saiya”, or Saiyans.
Nappa is a naturally bald Saiyan, and his Super Saiyan 3 design is a unique take on the transformation. Instead of the traditional spiky hair, Nappa's Super Saiyan 3 form gives him a long golden goatee.
Members of the extraterrestrial humanoid species known as the Saiyans (サイヤ人, Saiya-jin), Caulifla and Kale are the first female characters in the series outside of video games to have attained Super Saiyan forms.
In the anime, Super Saiyan Rosé is simply the standard Super Saiyan form for Goku Black, and it matches Super Saiyan Blue in strength. However, the manga states the form is the equivalent to Super Saiyan God Super Saiyan.
Kale's Super Saiyan (C-type). Because Kefla's transformation is a hybrid between Caulifla's regular Super Saiyan form and Kale's Super Saiyan (C-type), it is noticeably different. Her hair is green, she retains her pupils, and she undergoes a slight increase in muscle mass; but she does not grow in height at all.
Trunks' Hair Color Makes Him the Rarest Saiyan of All
In Dragon Ball chapter 333 by Akira Toriyama, Trunks has arrived in the past from his alternate future with a warning about the impending threat of the Androids.
Goku This Is the Result of My Training!" Super Saiyan Blue ( 超 スーパー サイヤ 人 じん ブルー, Sūpā Saiya-jin Burū), also known as Super Saiyan God Super Saiyan ( 超 スーパー サイヤ 人 じん ゴッド 超 スーパー サイヤ 人 じん , Sūpā Saiya-jin Goddo Sūpā Saiya-jin), is a powerful divine transformation and a transcended version of the Super Saiyan God form.
Akira Toriyama when asked why Goten and Trunks don't have tails, he stated that tails are a recessive trait. Which basically means that when it comes to hybrid saiyans, the chances of them having a tail is low. Gohan is simply a very rare case.