Thanks for the comment. You are correct that nothing "special" is done to distinguish these, and I can't say I ever thought of this as an issue, so thank you for bringing it to my attention

Not fully sure what I can do as the tiles just use the art from the physical game. Personally I think they're distinguishable enough to not interfere with the game, especially as:
- there are tooltips on each location which tell you what they are and give related info
- whenever you are about to build/move a unit the locations you can choose are highlighted (and barbarian villages are illegal locations for this as well), so there's no misclick risk

But I appreciate everyone is different, including in visual perception, so please don't think I'm dismissing this out of hand. If the above points don't satisfy you and you think this could cause real issues in a game, please let me know - particularly if you have any suggestions for visual changes which would help you on this issue.