This brings Color Vision to a whole new level. You show a large box (approx. 3 1/2 " sq.) with a multicolored die in it. They put the die into the box with a color side up or down, replace the lid (your back is turned) and gives the box to you. You can tell them their color. The standard trick ends there.
You show that the large die has a door and a hollow center. You place 4 balls into a bag. Without you looking, they take one ball and place it into the die, and placed the die into the box.
You take the box and........yes, you not only tell them the color up on the die, but you also tell them the color of the ball inside the die. Great for even large audiences.