We have run into a problem, that I think a lot of people using Unity face.
We would like to have control over the shadow color. For example in the desert scene, and we would like to add more blue in the shadows but without effecting the illuminated areas. Kinda like Anubis in Overwatch. Picture: http://edge.alluremedia.com.au/m/k/2014/11/Screen-Shot-2014-11-08-at-7.50.47-AM.png
We can't use a custom shader, because we use a lot of different shaders and for the ground we use another asset from the store. Our own shaders does include a shadow color that we can tweak. But we need to change the shadow on everything.
Ambient light you say? No that's not gonna work because it influences the illuminated areas as well which means that is getting washed out and it looses the vibrant colors, which we don't want.
What we're left with is maybe to render out a render pass with the shadows, that we could then tweak like you would do in compositing of a film. But I havn't been able to find any information about this being possible. And we don't know how we should do it.
sorry it's a bit of a late reply to this by now, and you've probably already figured it out, but do you know about camera effects to do post processing of colour such as Amplify Colour (https://www.assetstore.unity3d.com/en/#
!/content/1894) or other similar assets. It's pretty much the same process as most movies use these days and allows you to tweak the colours in your scene without actually touching the textures or lights in the scene. I think that's what you were looking for? I'm sure Overwatch would be using something like this, as do many modern games. You can make your own colour correction texture, or download some packs of pre-made ones, but it's pretty easy to make your own based on a screenshot of your own game and tweak the colours in Photoshop.
The ground texture blending stuff looks great by the way