Matt glaze of the slides

Use the main master slide, you can change to whatever color you want. Only RGB or hexadecimal are possible with the color wheel.

Hope you are aware that the way it will look will depend largely on the devices used? Captivate is about eLearning, not about printing where indeed this can be important. Moreover I will rarely use a pure white for eLearning, too tiring for eyes when looking at a bright white screen all the time. Just my personal opinion.