ColorMatrixColorFilter颜色过滤（离线用户的灰色头像处理）

Drawable mDrawable = context.getResources().getDrawable(R.drawable.face_icon);   
//Make this drawable mutable.   
//A mutable drawable is guaranteed to not share its state with any other drawable.   
mDrawable.mutate();   
ColorMatrix cm = new ColorMatrix();   
cm.setSaturation(0);   
ColorMatrixColorFilter cf = new ColorMatrixColorFilter(cm);   
mDrawable.setColorFilter(cf);