I'm building a piece of software which will have a filtering system that involves multiple flags. The complication is that each flag has three possible states:

1. On
2. Off
3. N/A (i.e. It can't be applied, for whatever reason)

Here's my current plan:

![enter image description here](https://i.stack.imgur.com/xPbFC.png)

So the "Size" and "Weight" flags are "on", "Height" is off and "Lid Width" is N/A (None of the products actually have a lid). Clicking each box toggles the flag, unless it is N/A.

However this method has it's limitations: One of which is that it relies on colour, preventing use by colour-blind users. I could use checkboxes instead, but they take longer to read and absorb when there are a lot visible at once.

N.B. The software will *only* be used by a small selection of experts for many hours a day. So it is less important for it to be easy to learn, and more important for it to be quick to use and visually clear what's going on at all times.