Look at doing the CounterBalance steel support system. But, it's not the counter fabricator's place to install counter support. It's the cabinet installer's job. You do NOT want counter fabricators touching your cabinets. At all.

We used Fastcap's Stealth Speed Braces to support the 12" overhang on our new Cambria quartz countertops. The braces are not visible, and no banged up knees when seated at the eating bar. Love 'em!

Here is a link that might be useful: Fastcap Stealth Speed Brace

Thank you! Since I see the "cabinet installer" whenever I look in the mirror, I'll speak with that person. :)

Here is our support:

This bar system was installed by the granite fabricator/installer. He routed a channel into the top of the cabinets the exact depth of the bar so the granite sits flat on top of the cabinets. You never have your knees bashing into a support. We, too, did our own cabinet installation and this was not in our skill set. The granite guy does it all the time.

I was unclear on your rainbow description, but just in case you were asking about another kind of a support, here is where our granite crosses the open space over the dishwasher and butts into the side of the pantry: