c# - Error System.Windows.Media.Color.A.get -

i have project image editor , erroneous reference markets 'system.windows.media.color.a.get' , not because make mistake brand error code in visual studio 2012 windows phone 8

would appreciate help

        public writeablebitmap process(writeablebitmap input)     {         var result = new writeablebitmap(input.pixelwidth, input.pixelheight);         var resultpixels = result.pixels;         var inputpixels = input.pixels;         var ta = color.a;         var tr = color.r;         var tg = color.g;         var tb = color.b;          (int = 0; < inputpixels.length; i++)         {             var c = inputpixels[i];             var = (byte)(c >> 24);             var r = (byte)(c >> 16);             var g = (byte)(c >> 8);             var b = (byte)(c);              int gray = (r * 6966 + g * 23436 + b * 2366) >> 15;              = (byte)((a    * ta) >> 8);             r = (byte)((gray * ta) >> 8);             g = (byte)((gray * ta) >> 8);             b = (byte)((gray * ta) >> 8);              resultpixels[i] = (a << 24) |                 (r << 16) |                 (g << 8) |                 b;         }         return result;     } 

what expected below lines?

var ta = color.a; var tr = color.r; var tg = color.g; var tb = color.b; 

according error using system.windows.media.color class , properties called 'a,r,g,b' public properties call static properties. if need access non static property need create object of it.