Some may have already discovered this but it appears to be undocumented.
If you create a local adjustment with for example, a control line, the mask will probably be coloured according to your “Color overlay” settings. Then to display in B&W, you select “Black & White” in the drop down. Or vice versa.
I find that I can toggle between the two by entering C or B on the keyboard. Fabulous. I requested this in feedback to DxO - it must have gone under the radar as a minor fix.
NO – no such hotkey “C” or “B” (checked in PL7.8.0_254),
but still this annoying & time consuming mask
while the online help shows the former and much better behaviour.
Yes there is but annoyingly it does not work first time. If you toggle the mask colour one time then it works after that.
I didn’t notice this as I discovered it accidentally after manually switching the colour.
Oh well, thanks but no thanks DxO - this is broken.
Mask View mode ( as a supplement … )
I was hoping to stop seeing this silly “permanent” mask mode (= introduced with PL7.5.0 Build 176) that appears unless adjustments are made. This doesn’t make editing easier or safer, it just creates additional and unnecessary mouse actions.
Additionally, the previous mask layout
is quicker to use. – To switch from color mask mode to black and white/grayscale display, I only have to click once (and no drop down to then choose …).
And – can’t we get an option that allows the user to pre-select which tools will be displayed with which mask types? This would make the whole handling much more pleasant.
Similar as with Nik 7, it is easier if, for example, the black and white/grayscale mask appears when setting control points – however, when using the brush or auto masking, the color masking.
For a pleasant UX let the user customize how he/she wants to work!
Indeed the result on the C and B keys is completely random.
I know this thread is marked for Windows but here is a screenshot that shows that the Mac version is totally different, with no shortcuts for swapping masks
It’s the same on the Windows version, there is no information on these keys.
To make it work, I have to modify the first time via the drop down list and then the C and B keys allow you to switch between color or black and white masks.
And if I press C or B too fast, the keys don’t work.
Actually, it’s not “keyboard shortcuts” that are functioning in this case … what you’re simply seeing/experiencing is “quick jump” selection between the drop-down options.
That’s why (as you say) you need to “modify the first time via the drop down list” - the result of which is to apply focus to the drop-down control; 
Thereafter (UNTIL you redirect focus to any different control), by pressing the “C” and “B” keys you’re alternating selection of these drop-down options - according to their initial letters
That’s why this apparent feature does not work in all cases - since the “quick jump” selection operates ONLY when the drop-down has operating system focus.
And in the previous version one did NOT have to
but simply click the checkbox once, if one wanted a B&W mask.
Otherwise the color mask was preselected – 1x click and simple to understand.
