Applying Rules for the selected cells, like background color, text color provide me with a nice colored box I can type some 'Legend' elements into, but it's still within the table and not movable to another position (another corner of the page, etc.) or a sidebar.
I just exported the doc to Excel, and immediately, right there in the Insert Tab, was a choice called Text Box, which I can insert anywhere on my spreadsheet, including a sidebar that is not within the columns, or the space in the upper left-hand corner between the columns header and the row names. I can add ant text or symbols I want and color-format them, creating what can be a true separate Legend.
It's not that I wanted something that feels just like Excel; just wanted to be able to create this Legend, in Numbers. I understand Numbers is not Excel and doesn't offer the exact same choices...but not being able to find this easy-peasy insert anywhere in Numbers is just unergonomic, jumping through too many hoops, and a huge oversight in my opinion. Having an easily inserted Legend is a common need in spreadsheets/tables as well as charts.
Fortunately, I'm subscribed to MS Office 365 n all my devices, and can dump Numbers and go back to Excel. I wanted to support Apple and give Numbers a chance, but...this is too big an obvious ommission