Terrain texture colors are off since 3.8

[lukaspj]

As detailed by @Bloodknight here, the terrain textures seem slightly off in color. It's more pronounced the more detailed the textures become.
The major issue with this, is that it complicates the use of detail-textures as the close-up color contributor for terrains.

3.8:

3.9/3.10:

[lukaspj]

An example of a shader from #2049 can be seen here:
https://gist.github.com/lukaspj/ecd9d46426889c611a565b6edde12572

Not much has changed since 3.8, in terms of computation of color. The major thing would be linearization, which I would believe is the culprit.

My guess would be that grayscale = don't use toLinear, as it is a lighting effect, but color = use toLinear as it is a diffuse texture. Detail textures sort of acts both ways, thus it both should and shouldn't be linearized, and that could throw the math off. That would explain why gray-scales seem unaffected by this issue, as far as I know at least.

[Areloch]

Solved via #2051