So what I’m thinking here is the blue tile outline which designates multiple items on one tile is very useful and could be expanded to denote a wide variety of other useful information. For example, you can’t currently tell if a zombie or vehicle is on fire without putting your cursor over their tile, which will then show you the relevant information. Acid field visibility is also blocked by items and bodies on the ground. To fix this, you just need to put a colored outline around the given tile to quickly show you if there’s fire or acid on the tile in question.
This system could also be used to give information about things like status effects or hostile alerts. For example, a stunned or downed status might cause a blinking yellow outline. Or when movement is blocked by safe mode, all hostiles get a red outline on their tiles. Or perhaps a white outline if you are using a flashlight in daylight? Just to name a few of many, many possible uses for this feature.