Small white dot algae growing on glass?

It could be.. but with my tank it either comes in green or red depending on where in the tank it is cropping up and under what intensity of the light it is getting. Also mine doesn't come in that perfectly round either. I'm not saying its not, but is it hard to remove?? Like you have to use your fingernail to scrape it off? Or does it remove easily?

Like I said a macro picture would help.
 
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