Different colours for damage numbers

[tqFan]

What does the different coloring on damage numbers mean?

I’m playing with a Lightning Savagery Druid and i have reached some really high damage numbers on crits against enemies on Elite. I often see the numbers being colored differently when i hit with a crit. What does that mean? Is it some kinda threshold indicating that i’m overkilling enemies too hard? Or is it some other indicator that i’m not aware of (like an enemy being more vulnerable to my damage type)?