In this Adobe Premiere Pro tutorial, I'll show you how to use the mask controls on the Ultra Key effect to stack multiple instances of Ultra Key in order to key out different colors of green screen. This is a great technique for getting a perfect key, even when you have multiple colors of green screen in your footage.

Here are the steps:

1. Add an instance of Ultra Key to the green screen footage.
2. Use the Ultra Key pen tool to mask out any areas of the footage that you don't want to be keyed out.
3. Duplicate the Ultra Key effect.
4. Reset the settings of the duplicated Ultra Key effect.
5. Use the eyedropper tool to select the color of the background that you want to key out.
6. Adjust the settings of the Ultra Key effect until you get a good key.
7. Use the opacity mask to finetune the key.

Here are some tips:

* Use the pedestal control to reduce noise in the background.
* Use the shadows and highlights controls to adjust the brightness of the keyed areas.
* Use the contrast control to improve the definition of the keyed areas.
* Use the midpoint control to adjust the color range of the key.
* Use the tolerance control to finetune the edge of the key.

How can you stack multiple Ultra Key effects on one clip in Premeire Pro? You can use the mask effect on the Ultra Key to mask out one instance of the effect so it doesn't change the color of the rest of the clip, then you can add another instance of Ultra Key to the clip in Premiere Pro.

This allows you to key out difficult to key clips that might have multiple colors in the green screen.