A strange discrepancy between LuaTeX and XeTeX

My wine list, previously referred to, include the following font definition —

\font \vfont = "ITC Zapf Chancery"/B:color=007700;embolden=4;slant=-0.1 at 11pt

In XeTeX, characters set in this font appear as intended (green, emboldened, slight slant).  In LuaTeX, they appear green-with-black-stroke, emboldened, slight slant.  Does anyone have any idea from whence the black stroke is coming ?

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Philip Taylor

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