That is an excellent point, I'll add to that. The con system is a good topic to go over on Homecoming Wiki. https://homecoming.wiki/wiki/Con_System
As much as possible, grey, green and blue mobs is a sign to move on from an area. The XP will be reduced, and it will take a long time to add to your bubbles. There's a dark grey that is -4 or less combat level to your character. When dark grey mobs are defeated you won't gain any XP or inf, no matter how many you defeat.
Also, an area with nothing but red and purple enemies (fuchsia really) is a sign you might be dancing with danger a little too much. XP is amazing but unless you're with a team the debt isn't worth it.
Giant Monsters always con purple and can land in any zone (Winter, it's practically guaranteed.) Never solo a Giant Monster unless you're Level 50 and you made a build that focuses on defense and have a lot of resources to manage it (Inspirations, Temp Powers, and Incarnate powers.) Or, again, you're with a team or league ready to whittle it down bit by bit. (Always join a team or league if one forms to fight a giant monster! The XP and merit/aether reward isn't assured if you're not on the team and taking pot shots at it hoping to damage it enough to matter.)
The sweet spot when leveling is white, yellow, and orange, with some reds on occasion. If that's too much to remember at first, warm colors (yellows, reds and oranges) have XP, cooler colors (greens, blues, grey) have less. Purple is bad to solo. Well, maybe an occasional purple if you have lots of inspirations and you got a small team with you. Or a hospital close by.
It takes a while to get used to. But the more missions you do the easier it is to 'feel an area out' in a way.
