So now the question becomes: which key should I use instead?

Or it could be an account setting (but that involves a bit more work to implement).

It would be most instructive to gain some insight as to how a second colour would be of use :)

Honestly I was pretty surprised that , was getting hit inadvertently. None of the adjacent keys on a standard American keyboard do anything (other than space), right? So is this an international keyboard thing?




The key difference for me is that it could be used on cells that did not have a number in them. So I could quickly flag a given cage or all the locations that could have a 3 in the puzzle or do even/odd colorings (rarely needed, but I think I did do it once).

Not only: it is very useful when you have to calculate the total sum of an extended sub-group of cells in order to determine the value of a remaining cell or a group of cells, regardless if they are empty or already bolded.
Another use is to highlight a cell in which you put a "trial and error" value which could be clearly wrong only after a large number of steps, in order to start again from that value without forgetting it

So which key should I use instead?

I thought initially that the comma key was fine, only close to the space bar of course.

Maybe a letter key, like 'A' ?

A works for me
although I do not actually use the purple at this time :)

Patrick, 'A' would be great: it is easy to tap with the left thumb or the left forefinger

EDIT: No, 'A' is already used to insert '10' in the puzzles bigger than 9×9... Probably 'Z' would work better

Not against this particular feature, but there's a more general question:

If puzzlers accidentally touch a shortcut key that turns on a feature they didn't even know existed and aren't sure how to turn it off again, how should this be remedied? Of course they can turn to the forum (if they know how to use it) with questions like "Help! Something turned green/purple/bold, and I don't need/like it" and someone is going to help them, but that seems a bit random. Should there maybe be a sticky topic on special features and the shortcut keys that turn them on and off? That would have the added benefit of drawing more attention to the features themselves.

(Apologies if such a thing already exists; I'm not as attentive a user of the site and forums as I used to be.)

Z feels more likely to get hit inadvertently being right next to shift.

Honestly I thought the comma was pretty ideal.

Ah, forgot about that.

the T key maybe?