From what I can gather, the oil filter grey is very light, the grey used on the engine itself is very dark indeed, I have a sample card but it looks too dark to me.
As an aside, Im sure I have seen pics of Chevys where the fuel filter bowl (just the bowl, not the cast upper section) was the same shade of light grey as the oil filter. Would you agree? I think on CCKWs it may have been either OD or olive green (just my guess, not fact), if this is accurate maybe it has something to do with fuel filter positioning, ie; engine bay on CCKWs, under cab on G506s