Here you can specify the color for texts inside the graph, like Title text, co-ordinate text etc. It accepts hex RGB values of colors.
Here you can also specify a value 'Auto', this will let the program automatically determine the best visible color depending on background color and other factors.
On clicking this field a color picker box will pop open, where you can easily select your desired color.
Note:- Before using this feature you must enable the customize color option.