create a static method in xlnt::fill to create a solid fill with a particular color to be the cell's background color

include/xlnt/styles/fill.hpp

@@ -163,6 +163,14 @@ enum class XLNT_API fill_type
 class XLNT_API fill : public hashable
 {
 public:
+	/// <summary>
+	/// Helper method for the most common use case, setting the fill color of a cell to a single solid color.
+	/// The foreground and background colors of a fill are not the same as the foreground and background colors
+	/// of a cell. When setting a fill color in Excel, a new fill is created with the given color as the fill's
+	/// fgColor and index color number 64 as the bgColor. This method creates a fill in the same way.
+	/// </summary>
+	static fill solid(const color &fill_color);
+
 	/// <summary>
 	/// Constructs a fill initialized as a none-type pattern fill with no 
 	/// foreground or background colors.

source/styles/fill.cpp

@@ -194,6 +194,14 @@ std::unordered_map<double, color> gradient_fill::stops() const
 
 // fill
 
+fill fill::solid(const color &fill_color)
+{
+	return fill(xlnt::pattern_fill()
+		.type(xlnt::pattern_fill_type::solid)
+		.foreground(fill_color)
+		.background(indexed_color(64)));
+}
+
 fill::fill() : type_(fill_type::pattern)
 {
 }