Is "over-saturated" redundant?

For me, "saturated" implies there couldn't exist more of given quantity, like concentration of substance in a solution. So "over-saturated" (as in "over-saturated market") seems redundant.

Yes, but there's no getting around it. Saturated is used for things that can literally "hold" more than their saturation point now, for example color in color photographs.

Where color saturation could once be enhanced by means of filters with wonderful results (polarizing filters for the sky, and water, for example), today, someone has merely to keep clicking on a button in a photo-processing app to render color saturation richer and richer until (no, the photograph does not fail to accept anymore, which would be saturation) the photo can actually become grotesquely colored.

I would say that persan would need to cut back on the saturation. If asked why, I could only say, "It's over-saturated."