What the title says...
I think it does not exist ? Or did i miss it somewhere ?

The game is just to dark for my taste.
The map without fog of war is a bit too dark but bearable.

However the parts covered by the fog are completely black, so i have trouble to see where i explored already and where not. (Not to mention trouble finding settlement locations...)

A option would be to make the fog of war lighter (not remove it, just make the visual less dark).
Is it possible ?

I had the same problem... Link to http://forums.civfanatics.com/showthread.php?t=292414

I solved it for my purposes by chaning the Fog of War density. (XML\Art\GlobalArtDefines.xml::FOW_WAS_VISIBLE_COL OR).

It's still a wee bit too dark, but i can clearly see the explored terrain now.
There should/might be similar controls for the overall lightning in the XML files.