When I started making amigurumi I noticed that some not all had very cute blush. I also studied Artist Anime bears and they all were shaded to some degree. Loved the look but could not fathom how it was accomplished. High end Artist bears are airbrushed, giving fantastic 3 dimensional texture and I wanted to carry this technique over to Amis.. After much trial and error I've finally fond a application that is consistent and attractive. Most Importantly it is Simple.
You will need a Fabric paint pen in the color you desire, water and a q tip. I like to apply before I attach eyes. Simply wet your area that you want blushed then rub the pen lightly in the area. It will bleed so keep the color inside the center of the damp spot. You can also Smudge the area with you finger, but remember you now have paint on you finger :D
This Bunny is blushed only on the cheeks. In a more detailed piece with more facial detail I will darken behind the eyes and add blush above the nose and on the chin. I will also darken a little at the top of the embroidered nose to create a harder looking stop.
Play around with this technique and see what you like best. Your personal preferences will drive you to the best blushed Ami.