information – Legend of the grid: are there any rules on this?

I have a grid and I think to add a legend. As there are legends for the graphics.

Here is what would go into the legend:

  1. 70% of the columns are editable. The known model would be to put a pencil icon in each column. But I end up with an army of pencils … 🙂

  2. Some line items are missing data. I have to label them, so that the user knows.

  3. There is a column where the content can be added; unedited.

I thought about color coding these 3 things. But, come to think of it, I need a non-color dependent way to communicate this information., For the purposes of the ADA. So, I end up with icons, anyway …

Right? Ideas?