Created Unassigned: Background Cell Color [8860]

.Style.Fill.SetBackgroundColor() property sets the color pattern and not the background color :

public XLColor BackgroundColor
{
.....
get { return _patternColor; }
.....
_patternType = value.HasValue ? XLFillPatternValues.Solid : XLFillPatternValues.None;
_patternColor = new XLColor(value);
_patternBackgroundColor = new XLColor(value);
.....
}
}
}