re-format failed

[juneleung]

QXlsx::Format format;
if(fg){format = cell->format();}
format.setFont(newfont);
format.setPatternBackgroundColor(QColor(255,00,200));
xlsx.write(i, j, value, format);

in this code, I try to re-format the cell. if fg is true, setfont will not work but setcolor works. if fg is false, both work, that looks strange and I haven't found any solution, hoping for a guide about reformatting the cell.