Because Mars is about 1,5 times as far removed from the sun as Earth, it receives significantly less sunlight. However, in a game like Mars Commander, depending on the artistic feeling that you want to express, less light may not be the optimum solution. Realistic lighting made our environment look drab. The effect may have been good for horror games and the like, but it wasn't for a shooter and strategy game combination like ours.

As a designer, you want your game to be inviting to play, and good lighting is a way to achieve this effect. In  Mars Commander, this meant boosting the game's directional light. (In most cases, directional Light is what Unity uses to simulate sunlight). Other games, such as platformers or cell shaded games sometimes take this effect to a much more extreme level, but we thought it best to remain subtle in our case. 

Directional light color was another factor to consider. At first, we tried colors that fit our color scheme, but that did not provide us with a very clean look. However, conversely, white light, which is what you would find here on Earth in reality, didn't quite have the right qualities either. A subtle shade of red is what we decided on in the end. 

Mars has a lot of indirect light bouncing around. Indirect light is light that is one or more steps removed from direct light, which is what the sun beams onto us from beyond the atmosphere. We thought it best to simulate this effect with reasonable accuracy, though we ended up boosting it a little too. For fellow developers, a great tool for creating proper indirect light is Radiant Global Illumination by Kronnect, which you can find out more about here: https://assetstore.unity.com/packages/vfx/shaders/fullscreen-camera-effects/radiant-global-illumination-225934

The sky itself was another factor t consider, as we had various options at our disposal. In reality, the Martian sky is a dusty red or brownish color during the daytime, which is rather similar to the color of the crust itself. We had to tweak these colors, as contrast is an important factor in environment design, and perhaps art as a whole. You want your sky and your terrain to be at least reasonably different in appearance, so that the player can easily distinguish between the two. In the case of Mars Commander, we ended up making the sky darker and less prominent, thus contrasting nicely with the boosted colors of the terrain. 

Other types of terrain may lead to entirely different considerations and artistic effects. Looking into the future, this may even be the case for Mars Commander, as we are definitely considering expanding our horizons beyond the Red Planet at some point. But until then, the above should serve us well.