Just had to desaturate a clip and then return it to normal. Code wise it’s rather simple, the following turns a MovieClip with an instance name of test to grey:
// Make Grey
var r:Number=0.212671;
var g:Number=0.715160;
var b:Number=0.072169;
var matrix:Array = [];
matrix = matrix.concat([r, g, b, 0, 0]);// red
matrix = matrix.concat([r, g, b, 0, 0]);// green
matrix = matrix.concat([r, g, b, 0, 0]);// blue
matrix = matrix.concat([0, 0, 0, 1, 0]);// alpha
test.filters = [new ColorMatrixFilter(matrix)];
To return it to the default state just clear the color matrix:
// Return to normal
test.filters = [new ColorMatrixFilter()];