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.
color of someone's money, see the
Prove that you can pay, as in Before we talk any more about this car, let's see the color of your money. This term probably originated in gambling or betting. [Slang; early 1900s]