Sorry if this is already posted. when I searched it appears that most people have a problem with the grayscale effect not working, mine is the opposite. In the portfolio editor options if I change the portfolio image hover effects to none instead fo the default grayscale. The grayscale hover effects still work. I can disable it in the css file but was just wondering why the feature options doesn’t take care of this. as I may want it for 4 columns but not 2 columns for example. I have been testing on a mac with safari and chrome.
Perhaps your install was buggy and you should re-install WordPress and the theme (while updating the theme first to latest version).
You can use css to turn of the effects on a per-page basis so you can still have the effect on one page and not have it on a different page. To do that check the <body> html tag of the page in question to see what css classes are specific to that particular page and add it to the front of whatever css you are using to remove the overlay.