Map Icons with color auras? What do they mean.

[Avatorn]

Why do some icons sometimes have colored auras? (and sometimes the same icons don't).

I've seens purple and green (usually on books, bags, and card icons, but again sometimes they're just grey, and sometimes these auras are on encounters, and no they dont signal obelisk corruption). I've also seen goldish-orange auras and red auras.

Not really sure why tiles get auras and what they mean, nor can I find a key for the colors (just what the icons means).

[Fendelphi]

The different colour icons on the map indicates how rare an event is.

Even though the map itself is static, some nodes can have different random events. If you get a blue or purple, it is a rather rare event and might yield some interesting rewards.