The difference between a Locker ON and OFF are:
Black / Grey ——> I do not care the color (I do not see the difference)
2 pixels… —— Can’t you dran it at 45° to the left ?
(at 72 dpi or 4 pixels at 144 dpi)
And that is when the graphics is displayed…
OK, this is cosmetic, but when I want to know, I have to take a magnifying glass…
OK, youngsters can recognize the state on ablink of an eye, but we are mostly oldsters here (> 40) where the contrast have to be important (between the text color - locker here - and the background color).
You asked a “contrast”, sooo… Those icons mix 3 concepts at once, design (locker closed/open), color (red/gren for a locked or free) and check sign (checked locked, not checked free). Most visual impairments covered, except myopia with color blindness and no glasses.
They use SFSymbols on the Mac and Bootstrap icons on Windows and Linux. I’ve added details of the padlock elements from both those sources to the feedback job.
Note the lines that reinforce the relationship between the object and its container. Also notice that the curved part of the lock swivels away from the body of the lock; this is a much better, higher visual contrast way to differentiate the two.
Those icons mix 3 concepts at once, design (locker closed/open), color (red/gren for a locked or free) and check sign (checked locked, not checked free). Most visual impairments covered, except myopia with color blindness and no glasses. 
