If you mean the difference between the color of a swamp and the color of a marsh, rather than "swamp cooler," then it sounds as though you are asking about the color of a marsh compared to the color of a swamp.
The definitions of 'swamp' and 'marsh' may be helpful to you.
Where did you hear or read these phrases and what is the context in which you saw or read them? It will help us to answer the question if you could give us some more information.
Hm I mean just speaking about shades and colours. In my native language we can say “The swamp colour” meaning the colour of a swamp (a forest wetland). The one I attached below
But now I guess, in English I can’t say like that.