I'm not sure either, but I'm going to guess it's because you still have the object selected after you applied the Subdivision Surface modifier. I usually deselect the object once the modifier has been applied, so my mesh usually turns what looks like solid black. The reason is because, once subdivided, there are so many more polys than there were before the subdivision, and I usually have to zoom in a bit closer to see the mesh better.

I can only assume the same is true of the UV layout, because it turns an orange/red color when the object is selected in the Edit mode window.

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OK . . . Where's my chocolate?

Butterfly Dezignz