Yeah, well, hover over it to see the Rainbow shader. Sorry. But only put Saturation on 1. Putting Luminosity on 1 will make it white, so control the scale to see how bright the rainbow shader will be.
Go to Rainb(ear)ow > Materials > No Name, and then select _Shaders on the Shader tab and you will see Rainbow. You can control how it looks on the tab.
If it's with the character's material, check if the shader is applied. The shader is animated so it will be paused (be pink) when editing/publishing the avatar on Unity and will be animated in game.