I have been designing instructions for years and really haven’t paid that much attention to “color theory”. I do use color to gain attention, such as by using red arrows or yellow highlights, but the images I have used in past instructions have been entirely of someone else’s creation rather than my own original work. As such, color was not something I had ever thought about previously. Most of my instructions are print-based PDF files. A few reside on the website but these are constrained to the design elements already in place by the site’s CSS files. I guess I consider color when creating PowerPoint presentations, but only to the extent of selecting an attractive theme.
The only time I pay much attention to color as a designer is when working with instructors on course design within the learning management system. Even then, Blackboard offers pre-built themes which can greatly simplify the use of color within a course. It is only when instructors delve into the use of color on their own without an understanding of color theory that I see problems arising.
I have seen Blackboard courses where the instructor used color in their design to the extreme. The result was distracting at best, and may have been disastrous for some learners. Pairing low contrast colors together makes reading menus or text items difficult or impossible. Some color combinations do not work at all for students with color-blindness. For students with low or no-vision, the use of color as the only visual clue to an instruction’s importance is problematic.
Visual design theory comes more naturally. Obviously, by off-setting the margins and using bullets or numbered lists, you can break up the monotony of a line of text and call attention to a particular text element. Offsetting that textual element with a border or color highlight further helps to call attention to it and feature it on the page. Balance is a little less natural, but the eye does tend to notice when one side of the page looks lop-sided and wants to do something to adjust things so as to create a sense of balance.
I am sure that the use of both color and design theory will become much more important as I design media instruction. Things like the rule of thirds; balance; contrasting colors, especially related to on-screen text; creating movement; drawing attention; all of this will become very important as I design for media. Whether that media relates to still images pieced into a slide show, animation, or a full-motion video, I think the same principles apply.