That the seller should be honest and say it has been relumed and save himself from embarrassment/lost deals.
I'd need to see it. My -76 is all original and depending on the light can be olive green, copper oxidation green, or yellowed.
Considering yours is original , I think it very attractive. Normally one would be suspiscious of such a tone but yours is fortunately evenly matched with the indices .
A lot of -76 and -78 reference dials have greenish Tritium indexes, that's a common thing. Those green hands have been relumed with superluminova IMHO. An UV test should immediately confirm that
I've seen Speedmasters as far back as -71 models with hands that were perhaps a tad less green than these, and upon close inspection appeared to be original. For these I would do the standard lume test, to see how long they remain illuminated. However, given the state of lume on the dial (not just faded but mostly gone) I'd say these are probably replacement hands from a while back.
Makes sense... as the crown might also have been changed... or did come with the 105.012-66 watch delivered in late 1968