ill tell you just click this Find mods by clicking here. it will take you to all the mods for desktop goose in GitHub don't worry you don't need a account any ways this is rainbowstrobe click here to download it RainbowStrobe (default mod) open desktop goose folder then go to assets>mods, then create a new folder then move everything in the rainbow strobe into the folder you created but not the downloader like WinRAR or somthing like that then rename the folder Rainbow strobe then run the goose then your goose should be rainbow 
Oh and do what i told you to do with the rest of the mods