I've though about this a lot.
Although not every RWR game has tons of people, there are many times when working directly with others that some slightly more noticeable and specific marker should be used.

The current color palette used for the markers is perfect, and fits the overall toned-down color scheme of the game quite well (Although Black is actually difficult to see most often on the field)

I'd also like the addition, if possible, while in game to open the menu with some quick easy option to invite, or add people to your "squad". Or whatever works for RWR, for me it doesn't have to be Steam related.

So I was thinking that a standard allied bright green could be supplemented for the random default colors. And seen by those in the squad itself only. There is nothing overly bright used at this time, and this simple change in color could allow you to quickly locate the few other specific people you are working with.

My only personal concern for this mechanic is that is may have the unintended effect of causing people to work less together over all in the heat of battle. As it is now, when you fight you can easily distinguish real players from the AI, but often don't have much time to constantly recheck names while your next to someone. And with the frequent deaths in RWR that slightly yellow guy next to you dies, and then next slightly yellow guy you see may not be the same one. Or red, or blue, or whatever. So over time players naturally work together as a whole team without regard to who is next to them long as we all survive together.

Yet still I'd like to be able to squad-up and work specifically as a fire-team with a few others.

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Footage

The friend locator and the player squad forming is indeed somewhat related, or overlapping at least.

Some vague ideas for the player squad forming feature have been that you'd be able to, again, tag another player in someway. The two fairly straightforward ways could be to press LMB + a modifier key on a player soldier, and, by doing the same in the player list (scoreboard).

On such event, the server would make you join the targeted player's squad. This could for example be visible by aligning your marker color to the leader's marker's hue, maybe with some difference in brightness to make you stand out a bit from his. Would be also simple to add a marker color chooser (or a /color #rrggbb style chat command for prototyping) so that the leader could also control the squad color, in case two hot pink leaders would be working in the same area.

If the leader marker color had a unique tone in the match, locating other squad members would be simple, regardless if you were looking at the field view, map view or screen edges for marker colors. All blue markers would be your buddies if you were one of them. Additional highlighting could be added as well, scaling their edge / map markers bigger, using different icons, etc.

As Steam friends list idea has the overlap of using marker colors or shapes or specific icons, there would either have to be two different ways to highlight these things (sounds messy), possibly one taking precedence over the other, or these two things could be combined. Maybe there would be a button/command somewhere which would create a squad out of the friends in your list, those friends who are not already in another squad, or it could be just sending out private messages to the friends requesting them to join your squad the usual way.