Foreword I have no idea if any of this is possible: one solution might be for enemy units to have a different line colour on their map markers.
e.g it is a style where the differentiation is mainly on separation of enemies from allies in large scale conflict.
Icons with distinct team based outlines, but flat internal colours, e.g the light icons are team 1 vs the dark icons team 2. This would have the added advantage of being able to use black as a colour.
Alternatively, ALL enemy units are given the same line colour (e.g red or something chosen by a player), but have distinct inner colours. Having a different outline for an enemy can potentially help to distinguish an enemy dark green from a friendly teal.
Here is the current grey, but with a few red lines which would indicate grey enemies.