It would seem, that inverting the colour changes the invisible dot. Also, I checked the animation, when it was still, and there is no green dot, and the grey background it completely colourless.
But what I found though, is that the invisible dot, is the inverted version of the visible dots.
Oh, and yes, this illusion is old. I believe I saw it first about 4 years back.
edit: by the way, this version requires a bit more concentration.
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