Question: I often find myself changing text colors to the same color for five minutes at a time which is really unnecessarily mouse-intensive.

Answer: 
If the last action that you made was to apply the color then use Redo `Ctrl` + `y`
No there is not. But you can try following topic? maybe it will be a solution for you, to override some keys on new ones.

<https://productforums.google.com/forum/?hl=en#!category-topic/docs/docs-community/lOia0JT4dX4>