So what do the colors on character and item cards represent?

The colours refer to their gear level. If you look closely you'll also notice each colour has different stages because they have little notches around the inner edge of the circle.

From memory, gear level goes:

Level 1: Plain white border.
Level 2: Plain green border.
Level 3: Green border with 2 notches (one on either side).
Level 4: Blue border with 2 notches (one on either side).
Level 5: Blue border with 4 notches (2 on either side).
Level 6: Blue border with 6 notches (3 on either side).
Level 7: Purple border with 6 notches (3 on either side).
Level 8: Purple border with 6 notches (3 on either side), but now with a connecting line between 2 notches on either side. Hard to explain but you'll know what I mean if you see it.

I haven't seen Level 9 gear and above yet as I think the requirements are beyond the current level cap of 60.

What this all means is, if two of the same character are level 60 and one player has gear level 7 while the other only has gear level 4 then the one at level 7 will be stronger due to the gear upgrades giving extra stats.

"Slushie;2286" wrote:
The colours refer to their gear level. If you look closely you'll also notice each colour has different stages because they have little notches around the inner edge of the circle.

From memory, gear level goes:

Level 1: Plain white border.
Level 2: Plain green border.
Level 3: Green border with 2 notches (one on either side).
Level 4: Blue border with 2 notches (one on either side).
Level 5: Blue border with 4 notches (2 on either side).
Level 6: Blue border with 6 notches (3 on either side).
Level 7: Purple border with 6 notches (3 on either side).
Level 8: Purple border with 6 notches (3 on either side), but now with a connecting line between 2 notches on either side. Hard to explain but you'll know what I mean if you see it.

I haven't seen Level 9 gear and above yet as I think the requirements are beyond the current level cap of 60.

What this all means is, if two of the same character are level 60 and one player has gear level 7 while the other only has gear level 4 then the one at level 7 will be stronger due to the gear upgrades giving extra stats.

A very informative and eloquent reply. Thank you everyone!