The normal keywords OR syntax is
case (black, blue, red)
which will find items that include black OR blue OR red in the title.
Some users have been using this OR syntax for negative/exclude keywords. (doesn’t contain black OR blue OR red):
case -(black, blue, red)
We recommend that you use this single word format for maximum forward compatibility with eBay since the group format has not always been supported:
case -black -blue -red
The two formats are functionally the same. Our system and eBay currently support both forms.