Square D QO Breaker - Yellow vs. Black

[LG63]

I'm re-configuring an older Square D breaker box that uses QO breakers. In the process of looking for new breakers I noticed a bunch used breakers on ebay listed as "black face" or "yellow face". I thought a google search would turn up the difference between the two but the black or yellow reference seems to only appear in ebay listings.

So what's the difference?

 

[Mr_fixit]

new and old. newer ones have the yellow square d symbol, very old ones have black square d symbol, so they're all black. my guess, you might be talking 10 years they've been using the yellow, and older than that no yellow.

crappy picture. newer style on left.