Animation Guidelines are created from thebutton in the toolbox, like other placeholders.
When creating a new animation guideline, you can choose between the good old String type OR Color - a single, solid color or a gradient of two colors. Use this function to impact the color of a layer (shape, text, etc.) dynamically.
Animation guidelines tend to be shared across all the scenes in a program (think about the brand colors) - instead of creating the same animation guidelines over and over again, you can create them once in the Master Scene and they will be available to the animator in each and every scene. Follow the three steps outlined in the following image to edit an animation guideline.