I must have done something without knowing it. The question is just what? Suddenly all my green labeled photos in LR are no longer labeled green. The green colour on the actual photos is gone, but in the right column under "metadata" - "label" it still says green in writing. What did I do to suddenly remove the colour? And it's from all my photos!
Possibly you've changed the Label Set. In Library, go to the Metadata menu>Color Label Set to see what set is assigned. If you've never changed it before, Lightroom Default is probably the one that should be selected.