Could be a lot of things, I guess. First I'd ask, was the plan sitting in the same room that you shot the red in after you wet sanded it? This sort of thing happened to me once. I shot red trim on a plane then shot some clear over the trim. I was shocked when I came back and all the areas I had shot the clear were slightly tinted red. Fact is, there was red, what, dust I guess in the air from shooting the red trim. I probably should have cleaned the area and the plane before I shot the clear. But the dust stuck to the plane and the clear made is sort of look tinted.
In this case, could be after you sanded and "opened" the surface, dust in the air from the red paint drifted onto it and since the surface had been roughed with sanding, gave some area for the dust to catch. I'd say try cleaning it really well and lightly sand it again and see if the red tint goes away. If not, could be that you got some sort of contamination in the clear you shot.