From The Universe Divided, 10 Worst Microsoft Excel Practices.
4. Using color to indicate meta data
Using a color to indicate something is great if you are the only person using the Excel file. That is hardly ever the case. You would have to explain: ‘well, red means this row is to be deleted, yellow means it’s not checked, and green means it is checked’. That’s nice, thank you, but the sheet looks but ugly, and if I print this on black and white all that information is suddenly lost.
I agree with most of this list, but I’m not sure what the ‘worst practice’ in #6 is. What I really like about this article is the way he formats his formulas in the text – light brown background and small border.