it would be great if I can export the palette to a png!

Add an export option for adobe photoshop swatch/palette .aco format.

How do I change back to retro UI?

Opposite Hue shift

Nice, but I wish I could set the starting color

great idea , but just a thought what about if you could have an option to upload an image to replace the one is shown, so you able to see the diffrence in a fly on the image you may want to work with, & an opiton to download that pallet to use with ex ps