As pointed out by Robert, a lot of the unfinished look after sanding Micarta is the fibers that make up the material. Canvas and burlap are the worst.
What makes the dull or whitish look is the frayed ends of the phenolic impregnated material the Micarta was made from. The trick is to sand it smooth to a fine grit and then "fill" the frayed fiber ends with something.
Many folks us a coating of baby oil, but most folks don't like an oiled knife handle (and it wears off). I am not a fan of this method.
The better method is to use a drying oil like Tung, teak, walnut, Watco, or any good quality dried oil type wood/gun finish.
Sand to 400-800, buff and clean the handle well. Then apply the finish (Teak oil or similar) and let it soak into the frayed fibers, wipe it off before it dried fully, and let it cure fully before a final super-fine sanding with 1000 grit and buffing.
As Bill pointed out, a final coat of buffed on hard wax, like Brix or carnauba, will make the handle look wonderful. However, it usually isn't necessary if you buff right.
Tip - The color coated 3-M sanding cloth-like papers are perfect for handle finishing and work really well on Micarta. A pack has 400 grit through 8000 grit.
