see the color of (one's) money
To view the money that one will pay with in order to verify that they have it. Sure I trust you—but I still want to see the color of your money so I know you're good for it.
see the color of someone's money
Fig. to verify that someone has money or has enough money. So, you want to make a bet? Not until I see the color of your money. I want to see the color of your money before we go any further with this business deal.