Question: 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.

Answer: 
Suggested solution:

![enter image description here](https://i.stack.imgur.com/bgc2R.png)

> 
> How should I visually represent multiple three-state flags? The
>  complication is that each flag has three possible states
> 
> 
> 

Means there are only two states "on/off" for the component, but component itself can be disabled or enabled. So it is enough to have two state switch.

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

Having that understanding it is possible to throw switch away and use ordinary check-boxes instead (preferred solution).

![enter image description here](https://i.stack.imgur.com/mXqQY.png)
Well, if you (rightly) don't rely on colours, you'll have to add another visual element. And I don't see the problem with using checkboxes (from Amazon.co.uk):

![Amazon Brand Filtering Grid](https://i.stack.imgur.com/kUKOh.png)

You can gray out non-available options.

Update
======

In respond to other posts, here's a comparison of all the ideas so far:

![Various options with regards to filter yes/no/disabled](https://i.stack.imgur.com/k2Ciz.png)