All these options already exist. If you go to your Settings Panel, you will see the following:
The most important one there is "Circle Whiteness" which is what you're asking for in your suggestion. Click on the 0% it goes to 10%, click again it goes to 20%, etc., etc., until you get to a whiteness level that lets you see the troops easily.
Some of the others can be helpful in various situations.
- If you play with "Map Opacity", it makes some of the darker maps easier to read.
- "Map Size" is useful in making big maps fit and making small maps easy to read.
- "Colour Codes" are useful on maps where the map colours camouflage the troop colours and make them hard to see. They're also necessary for colour-blind people. I always recommend that people play with the Circle Whiteness first and Map Opacity second. Unless you're colour-blind, Colour Codes are really a last resort.
"Text Map" can be used to check which terts connect to which, when the map image is ambiguous.