Interestingly i had a bit of maple to plane up the other day. My first time with maple. I ran it through the thicknesser ( after flattening with planer ) and there were little grey splodges that remained until I'd taken off maybe 3 or 4mm. Is that normal with maple?
Grey marks, small or extensive, may be a fungal stain. Sycamore, which is in in the same
Acer genus is also therefore a maple, and maples in general are susceptible to rapid fungal (mould) attack if the wood surface gets wet and isn't subsequently dried off pretty rapidly.
So, in answer to your question, properly dried and stored maple sold as prime quality (or similar descriptions such as the American designation FAS) will (should) in general be fungus stain free, clear of discolouration, and essentially bright and white, with the occasional exception of things like mineral streaks. I suspect it's possible your wood has got surface moisture on it at some point after it was dried and stored and this surface moisture lingered for a while encouraging mould growth. I've witnessed a few times (maybe six or ten times) mould discolouration, some very limited and other times quite extensive, develop on sycamore and hard maple in as little as about half an hour to an hour after the dry wood got plenty of surface moisture on it.
You may be able to pinpoint a potential source of the likely surface moisture in your case, or maybe not. Maybe, for example, the wood got rained on and you didn't immediately take steps to dry the surface? Slainte.
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