Just as you match clothing colors, the same design rule applies for color in slides. In other words, pick a color for your slides that matches a color from your visuals.
For slides where you have more than one color, it's important to make sure that your colors compliment one another. The following sites will help greatly.
If you like a particular color, copy the hex code and paste it as a "custom" color in Google just like we did in the color picking video