Randomize changes the colours and the light, but not the river itself. To generate a different river structure, build the wallpaper on your computer with another seed: see Use it, in the sidebar on the right, further down the page.
Press Randomize for a variation of your own, or set every colour by hand. This palette editor redraws the river as you go: its shape stays fixed (seed 6), and every control changes colour, light or the logo, the same inputs the program uses to build the whole theme.
Randomize changes the colours and the light, but not the river itself. To generate a different river structure, build the wallpaper on your computer with another seed: see Use it, in the sidebar on the right, further down the page.