So, I am attempting to make a simple graphics mod that makes heavy mud clearly visually distinguishable from light mud and no mud, simply by making all heavy mud hexes appear as a single uniform dark brown color. This is not intended to be fine art, just a temporary expedient until eventually someone with artistic inclination makes a map mod that makes heavy mud be actually clearly distinguishable from light mud and no mud, or alternatively until the game devs add some sort of map mode that makes heavy mud distinguishable from non-mud.
In doing this, so far I have been partly successful, but there are some graphical issues:

First of all, the selected hex which is circled in blue is light mud, whereas the hex to its north-east circled in green is heavy mud. That part seems to be at least more or less fine (though it doesn't look great, it is good enough to be functional for a handful of mud turns).
However, there are other areas (all over the place) such as the area circled in pink on the left side of the map, where everything is mud, but there are weird straight lines in places and also weird halos of clear terrain protruding, despite all the hexes there being heavy mud. Does anyone have any idea what is causing that and how to fix it?
The other problem is that the trees seem to still be protruding, and in places where there are a lot of trees, this can cover up the dark brown background and still is making it impossible to tell in some places whether there is light mud or heavy mud.
What I did to make this was to simply make the 3rd hex in all the files be dark brown, like this for example. That is the FOREST_001 file (it has a clear background in the actual file, but when I upload a screenshot it converts the background so it is appearing light green in the screenshot here):

I did the same thing for all the other files for clear, rough, woods, swamp, etc. That is all I did to try to make this, nothing less, nothing more. Anyone know what I need to do to fix the issues with the trees and the halos/weird straight areas?
If I can get these issues fixed, I could upload the files for this so that if other people have a problem telling what is heavy mud, they can use this if they are willing to tolerate the horrendous graphics.
FAQ #1: "But doesn't it look like s**t?"
Answer: Yes, that's kind of the point

FAQ #2: "Do you really want to play with something that looks so horrible?"
Answer: I would only use this for mud turns. First of all, if it is working right, it should look normal except when there is heavy mud (just for a small fraction of the game). But if it causes problems, I would just make a backup and only install this for use during heavy mud turns, and then go back to a better looking map for other turns.