Most links and things that people end up posting are scams on facebook. I don't click on anything unless I know for sure that it is a valid source. I very rarely go on facebook anymore because of how rampant the viruses are. I get at least one virus notification from one of my friends per week.
I would not have been fooled by the color change app, because when Facebook starts something new, they promote it heavily. If Facebook wanted me to change colors, they would have put something in my feed promoting it. Facebook knows that there are scams and they take steps to prevent fraud by notifying their users.
I wouldn't have been fooled because since the beginning, when Facebook was launched, the colors have been blue and white. The style of the site might have undergone small changes, but the color theme has never deviated from the traditional blue and white colors that have come to represent Facebook.
No I would not have been fooled by an app. I only trust a few different apps and would not have even considered getting this one to change my Facebook color. If I even had the urge to change my facebook color I would see if it was on the Facebook website in their options.