Engage the Word is intended to be functional. I made this system to record what I’ve learned and to help navigate the text while I’m preaching and teaching. This is not Where’s Waldo where we mark every place in the Bible where [fill-in-the-blank] is found. We are trying to SEE God's inspired Word on the page. Orange, purple and yellow are all outlining tools. The Bible is full of good/bad contrasts (i.e. do this / don’t do this), for which I used red and green. And since the Bible was not originally written in English, we often need to pay attention to words - blue. That’s just about it.
Here's a short example of the whole system in action in Exodus 3-4.