QGAmplitudeStyle is an option for
QGCreateAmp, which specifies the QGRAF style file for
generating the amplitudes. If you provide only the file name, they style
will be loaded from the standard directory containing style files
($QGStylesDirectory).
If you specify the full path, the style file will be loaded from
there. The default value is a custom style file for FeynCalc
"feyncalc.sty".