Resources for Visual Aids
Adobe Color Picker: Provides ways to pick colors and gauge the accessibility of the combination of colors, helping ensure appropriate contrast. While the site is aimed at web standards for accessibility, color combinations that are rated highly here will be accessible for slides as well.
Coolors: Use this site to generate random color palettes, or start from a color you want to use and identify colors that work well together.
Editing Google Slide Templates: Follow these directions to adjust a default template (or to create your own) that uses your chosen colors, font, etc.
Editing PowerPoint Templates: This site has guidance for altering the template settings in PowerPoint.