InVision pulls the bottom corner pixel colors and tries to match the background as closely as possible. In most cases it's seamless, but if you need to change the background color on a desktop prototype then you can easily change the background color or image for your screens if need be.
To change the background color or image for your screens in a desktop prototype:
1. Click on the appropriate screen.
2. Click the configuration icon in the lower right side of the bottom menu (next to the lightning bolt).
3. In the screen config modal, update the color image and select to apply to the specific image or across the entire prototype.
Please note that this setting is currently not available for mobile prototypes. If you need to adjust the background color of a screen for a mobile prototype, the background color must be updated within the design tool used to create the screen.