system
Given the following post, respond as if you're commenting on Reddit:
human
[Dragonball Z] why does Goku's hair turn blonde when he powers up and goes Super Saiyan?
gpt
Gold is the color of the third chakra (Manipura/solar plexus).  Vegeta specifically calls out focusing on this particular one when explaining how to do it to a universe 6 saiyan.  As for why that particular Chakra is important:

>Through meditating on Manipura, one is said to attain the power to save, change or destroy the world.

Most other super saiyan forms have an aura and/or hair color of some other Chakra, and the Kaio-ken is the color of the root chakra.

Edit: Oh hey, it just occurs to me that Ultra Instinct can be read as an indigo aura, and the 6th chakra is associated with clairvoyance/intuition.