I recently wrote a Cool Coin Showcase on Lincoln Matte Proof Cents made in 1909-1916.  Here is an example I found for 1912 in PCGS PR66+BN.  As shown in the images, the flashy cartwheel luster on both sides reveal clean surfaces of natural almond-bisque and desert sky blue when rotating under the light.  How difficult are these to find with such rich qualities?  Well, PCGS has only certified 3 in MS67 BN, none in RB or RD, 7 in MS66+ BN, 3 in MS66+ RB, none in RD.  CAC has certified no 1912 matte proofs of any color designation in MS67.  So this gorgeous example stands amongst the very best of its kind.  And because of the BN designation, it costs less than one half of the 3 in 66+RB and it is not clear whether these meet CAC expectations or how much R in the B they have.   
 
This coin is approved by CAC.
 
PCGS Cert. # 31399836