The only way for you to know for sure is to ask seller to take picture of the back of the dial. If it is gold there will be a gold marking in the back of the dial. Not sure seller will accept though.
Solid gold Omega dials I've seen are marked with "OM" (Or Massif) either side of the "SWISS MADE".
I'm not sure if all Omega solid gold dials followed this marking rule though.
And I suspect that this one has been redialed anyway.
the case is solid gold, but its condition just does not worth it... thanks all... still, the dial is a mystery, but I am almost sure it is not gold
Did you see a hallmark? The dial looks a bit like those slightly adventurously designed American cased Seamasters which were also available in gold filled varieties...