Checking to see if it is possible to color the Boss frames according to their friend/foe status?

Showing the health as a Red color for friends, and then mark friendly boss units (ones you need to heal, specifically) as green health bars?

I dont understand your setup, do you want red color for friendly players ?
You can create a second bar indicator configured to display a different color status (for example friendcolor instead of classcolor) and enable this bar indicator only for bosses. The friendcolor status allows to customize different colors for friends/enemies.
To display a specific indicator only for bosses, goto the "Load" tab in the indicator configuration and filter the indicator by "Unit Type", selecting "Bosses" units.

Oh! Sorry, I mistyped.

Basically I want enemy units in the Boss Unit list to be red health bars (or some easy way to denote they are hostile), and then any friendly units in the encounter to be green.

From what I could Friendcolor made everything green (the name makes sense).

Basically the issue is a Boss frames list grabs everything in the encounter that Blizzard lists with a boss id, so it shows both. As a healer, I really just care about the friendlies. As there is no way to filter out the hostile units, I'm trying to just mark them as less visually distracting, and make the friendly units more noticeable.

Despite the name, friendcolor makes hostiles red. (the color for friend and hostile units can be customized going to statuses/colors/friendcolor).
So if you simply want friends: green (players or bosses), hostiles: red (players or bosses) , you dont need to create a second bar indicator, simply use friendcolor status to colorize the main health bar.
If you want something more complex, like classcolor for players in raid, and red/green for bosses, you have to use two bar indicators, assign a different color status to each bar, and use the "load" tab to enable one bar indicator for player units and the other bar for bosses.