1. Theme vs standard vs custom colors
Theme: these will change depending on the theme colors of your PowerPoint file (Design > Colors to change the theme)
Standard: these colors are built-in to every PowerPoint file
[Tutorial]
The standard colors are different to the PowerPoint theme colors, in that they’re fixed, and won’t change automatically when you apply a new theme or copy slides into a new deck. This can be advantageous. Say you want to use color to convey meaning – using red for negative and green for positive is a common combination. Here, you’d want to use the standard colors, rather than theme colors, as the colors won’t change, and your meaning won’t get lost if things alter in the future.
The same is true with custom colors. Sometimes you may want to add a specific color into the slide. This might reflect another brand in the deck for instance. In any of the color menus, you can choose More Fill or Outline Colors from the drop-down menu, which reveals the same color options pop-up as before, allowing you to choose anything from the color wheel, or a specific RGB value. Again, these custom colors won’t change if you alter your color theme, so just be aware of any overuse.
[Demo]
Difference between theme, standard, and custom colours
Show where each is on the fill colour drop down
Show impact on coloured squares of changing colour theme
Use theme colours for consistency and also ease of changing
Custom: prefill with your most-used custom colors and use the eyedropper tool to paste color onto your new objects