A couple of people have mentioned this in the "Official Ancestral Update Issues"* thread as well as in the Steam forums**, but now that the cause seems more apparent, I thought that I'd create a separate thread on it. Please feel free to merge this if there was another separate thread that I missed.
With both the Vegetation Alpha option turned on and the Hide Foliage box unchecked, grasses and trees near the camera, if the camera is close to the ground, turn lighter than the other foliage on the screen. With either of those options changed, the effect goes away.
What this seems to mean is that the Vegetation Alpha effect is currently only active for a very small radius from the camera instead of everywhere in the field of view. VA working is the light effect we're seeing.
Here are some new screenshots I took that show the difference with each of these settings changed. Look at the difference in the tree leaves for trees near the camera vs. ones farther from the camera.
(Edit: sometimes, with Vegetation Alpha on and Hide Foliage off, the grasses just disappear instead of lighten)
*
https://forums.totalwar.com/discussion/comment/2183683#Comment_2183683**
https://steamcommunity.com/app/214950/discussions/0/1762481957313903654/ and
https://steamcommunity.com/app/214950/discussions/0/2572002906841593412/?ctp=4#c1762481957312329427
Comments
https://forums.totalwar.com/discussion/222774/graphical-bugs#latest
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