Curious how you got the rainbow gradient!

https://gyazo.com/586f2f4e76d9c82cfcaff579911f8be2
here's a quick showing of the layers as i turn them on! it's been a few years so i'll try to remember the process for you
the gradient was blotted in solid colours that i blurred some of the edges for and then i locked the layer and airbrushed the colours in.

https://gyazo.com/f670e6abb3b85ac64d57e1ab4224a30d here is the colours on their own with a white bg, they are at lowered opacity for some areas and higher opacity at others to create depth.

after the initial blotted in colours i added a few highlights to certain colours (layer 25) to make them look reflective, https://gyazo.com/267d8d25ca07c563b4c6bef293bf4fc3

the layer after that is just specks of the colours at full opacity

the luminosity layer is the coloured layers copy pasted and then i airbrush erased away from the highlights so it only made the areas with light reflective

it's cut off but the last layer is the overlay layer, which is just a few airbrushed yellows and greens/blues over the yellow and greens to give more of a glow in the silver base colour as well and make the colours pop a bit more

hope this helped!

That's so cool, thank you for taking the time to show off the process!