Original Post Title Question: ‘Can I create a Material Layer that adjusts the saturation of the layers below?’
Short answer: Yes, obviously. As demonstrated.
Detailed question was:
the overall color of the Google landscape is a bit washed out, and I want to increase its saturation a bit… Within a material layer, is it possible to create one that I could use to adjust the saturation to those below without sourcing a texture or anything?
So yes, the example setup I threw together in five minutes doesn’t use a texture mask and just adjusts the saturation of the incoming layer. Which is what Ken was asking for. Any idiot can look at that and know to replace the Vector parameter with a texture parameter if they want more control over where the saturation is adjusted (or use the Cartographic Polygon masking method in the Cesium tutorial).
Thirdly.
Try it. You won’t be able to modify other layer by a layer if you use the landscape’s default stuff unless you: a) know what you are doing. Which you prove time and time again you do not.
b) use specific layer types, since blend will not work to override a layer. c) actually act on the correct output, and d) use a custom layer node.
Try it. See just how “trivial” it is.
I have tried it, it’s literally as simple as using a Landscape Layer Sample node to modify the attributes of a different layer. Like so (this is, again, a simple example using desaturation, but the same principal can be applied to literally any material attribute by using the weight of the adjustment layer to drive lerps instead):