Start very general and become more refined. Before you begin any video project, select a few colors that you feel fit the tone of the piece. These colors will be the only colors you use throughout the video essay. Here are some examples to give you an idea of good color pallets and bad ones:
When building your color pallet there are three things to consider: hue, lightness and saturation. You can think of hue as what determines the base of the color. Lightness is how bright or dark the hue is and saturation is the strength of the color (black and white is 0% saturation)
These examples use color pallets that contain six colors, but you can theoretically get away with as little as two. Typically, six is a good number, any more and your video can begin to lose consistancy. It all depends on how you want to use color in your piece. When choosing your colors think about the use cases (Which will be the font color? What will the background be? Do I need two background colors? Two font colors?)
A helpful tool is Adobe's color website Adobe Color. It allows you to build color pallets using the same theories we just discussed as well as more complex ones. These colors can be saved and imported as 'swatches' into programs like After Effects, Photoshop and Illustrator.