It is important to note that with any air dry acrylic paint system that water color washes can be used to achieve nice color tints as long as these washes are sandwiched between something rich in binders. this can be layers of paint not so thinned with water or with a sealing medium of some sort such. If you thin your paints with more water it is also a must to use a good sealer when you finish your doll.
You will find the addition of mediums does increase the sheen of the paints. That seems to be a factor I have encountered with all artist grade mediums that contain binders in them to increase adhesion. If you have been a user of the BabyFX line of paints like myself, you will have experienced that those paints are wonderfully matte but when you add in their Sure Bond medium to increase adhesion you can get some sheen there as well.
I do find that the RebornFX matting liquid is awesome at cutting down on the sheen appearance and reducing any tackiness you may feel along the way from the mediums. I find I got the best results when I pounced or painted it onto the pieces rather than mixing it in with the paint mixes. I usually end up applying this product after every 3 or so layers of paint.
Here is my baby once I finished painting her and applying a layer of matting liquid. The next step will be to apply the RebornFX sealer over this which will reduce sheen and lock in the paints. After that I will let her cure a week or two and then give her a final varnish. These photos were taken with a flash.