You guys are too fast for me ;)

My solution which is similar to @cormullion's:

    hexToRGB[hex_String] :=Module[{RGB},
        RGB = StringCases[hex, 
           RegularExpression["^#(\\w{2})(\\w{2})(\\w{2})"] -> {"$1", "$2", 
            "$3"}] // Flatten;
        RGBColor[FromDigits[#, 16]/100 - 1 & /@ RGB]
    ]

    Graphics[{hexToRGB["#A4A4A4"], Disk[]}]

P.S.: Things are not always just `#000000` and `#FFFFFF`. It's mostly varying of shades of `#A4A4A4` :)

***EDIT***

PieChart of the sector angles proportional to {R, G, B}

    hexToPiechart =PieChart3D @@ {ToExpression@#/255. & /@ (StringCases[#, 
        RegularExpression["^#(\\w{2})(\\w{2})(\\w{2})"] -> {"16^^$1", 
          "16^^$2", "16^^$3"}])} &;


    hexToPiechart["#A4A4A4"]

![pie chart](https://i.sstatic.net/HZoMv.png)