Correcting color contrast issues within Canvas can be done with built-in tools.
Canvas
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Quick information on bullet and numbered lists in Canvas.
A brief how-to for adding images via the Canvas visual text box content selector.
Canvas has features for accessible tables. You can add header rows and columns in the GUI.
You can edit each closed caption from the closed captioning screen by simply clicking the pencil icon.
This method is easy. After importing captions simply go line by line correcting each line.