The Saboteur

From Wikipedia:

The player will be able to explore the open world Nazi-occupied Paris and some of the countryside and parts of Germany. Colour is a key element in the gameplay, and players will experience an Ōkami-esque style when entering certain parts of the city. In order to make that district coloured ("inspired") again, players must weaken the German forces occupying the area. In doing so, that district's citizens regain their hope, characterized by the "Will to Fight" (WtF) factor, a measure of public morale.

In areas with low WtF, the area is dark, with colour being various shades of grey (with the exception of several German flags, bright red and complete with swastikas), whereas in areas with high WtF, the area is vibrant and with full colour. WtF also affects gameplay, as in areas with low WtF, the area is filled with German soldiers who patrol in most places of the map in large numbers.
It is up to the player to return colour to areas of darkness.

In areas with high WtF, the Germans will not be completely evicted, but they will no longer be everywhere at once, and will primarily be centered around military bases, barracks, police stations, HQs, and other strategically important areas. In addition, the French people will play an active role in the struggle for areas with high WtF. For example, if Sean, the main character, gets in a fight with German patrols, allies like the French Resistance, Maquis, and even French passersby will intervene against the occupiers.

Throughout the game, players will upgrade their character in the form of "Perks". These will improve accuracy, ammo counts, damage and more. Perks are gained through actions, such as evading high alarm levels, sniping targets or demolishing a set number of German installations.

After you are introduced to the black marketeer Santos, you unlock weapons smugglers to buy weapons, ammunition, explosives, maps and other items. He also runs all of the garages in the story.

http://en.wikipedia.org/wiki/The_Saboteur_(2009_video_game)