Here are some informative links with information regarding what you are asking. However, I have also been unable to find a graphical legend.
From:
https://forums.frontier.co.uk/threads/ground-ops.609111/
Leading up to combat: ENEMIES!
Enemies are split into different categories:
Civilians - technicians, researchers, poor sods in civilian clothes that die in few bullets, as they have no shield equipment. They're also least dangerous in terms of security as they won't scan you, and won't ask you what you're doing in that building that you shouldn't have keys to (they do get irked if they catch you in restricted areas though, keep that in mind). They only get mildly annoyed when you come too close to them.
Commando - your bread and butter soldier. Armed with laser or bullet rifles, these guys are the medium of everything, in terms of damage and health. Not much to say about them.
Scouts - armed with carbines, these are the weakest of them all. Don't dismiss them as no danger however, they use both EMP and frag grenades as situation needs it, and even me, battle hardened veteran got blown up by a simple frag grenade just because I didn't watch my shields.
Snipers - now these guys are dangerous. They don Executioner rifles, and if you listened to what I said above, those hit super hard. If you stay in one spot, 1 shot removes your shield, 2nd removes your head. They also fight according to their role and stay behind. Luckily, plasma weapons are slow and easy to dodge, and they're also rather weak and easy to kill.
Strikers - I hate these guys. Armed with Intimidators, alias two tubes of death, they will push, flank, come as close as they can, if there is someone who will get in your back while you're covering behind your last piece of anything suitable and fight off 10 guys, it will be Strikers. And if you turn around and see two barrels in your face, you know it's over, especially with your shields down. How to fight them though? Simple, they have to come close, can't hurt you from far which gives you ample time before they come hug you, so they often die before they even get close to you.
Enforcers - walking tanks. Can't even call them any different. Armed with rocket launcher and on t5 level, tormentor that 2 shots you, these guys are embodiment of endurance. I have never seen anyone take a blast from tormentor into their head and survive, guess what? t5 Enforcer needs 3 of them. Insane, tough mothers that often take whole clip on high level, often providing you quick death. They're rather slow however, on account of their heavy gear. Not that it stops them much.
From:
https://elite-dangerous.fandom.com/wiki/Conflict_Zone_(On_Foot)
Combatants
Aside from Commanders who may use any weapons their suit choice permits, there are five main types of NPC combatants;
From:
https://elite-dangerous.fandom.com/wiki/On_Foot#NPC_Personnel
NPC Personnel
There are different types of NPC personnel that can be encountered at settlements or points of interest. Their role determines which weapons and tools they are carrying, and what level of security authorisation they have at the settlement where they are stationed.
Most NPC personnel belong to a particular faction, though some may be representatives of
Omnipol, a special interstellar law enforcement agency that is independent of the Galactic Superpowers. Omnipol personnel wear distinct white-and-blue outfits with 'OMNIPOL' emblazoned across the chestpiece, as opposed to whichever faction livery they would normally sport.