blue/gray ish tinge spots on leafs ?

for some reason one of my plants has a few spots on a few leafs that are grayish/blueish. don't have any idea what this could be, it almost looks like a slug was there or something maybe but i have no idea. will get pics if possible but can not atm. any ideas, thanx!

i have some purple spots on mine,, i think it might be because of a near frost night in late june,, but im not sure,, it could be phosphorus defeciency too,,,

yeah i cant really find any pics of this deficiency anywhere. they recently started to appear only a few days ago but seem to be spreading...=\

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so? are they showing signs of weakness since you found the coloration.. mine are still growing and now preflowering ,, its weird , i think its moisture stress!