I have red-green deficiency, so red and green both seem like they have a lot of white in them (I found out). For instance, green traffic lights actually look white-green to me without the glasses, and same for red. The sunglasses make them look like a pure, brilliant green or red with no white added.

I would describe it as a pretty big difference, it's not tiny, it's really obvious, and whenever I forget my sunglasses or can't wear them for whatever reason, the outdoors look really muted.

They won't work if you have complete color blindness, because there's no red-green distinguishing information to work off of.