I dunno about grain filler on maple. It is a tight closed grain, I believe. The site implies that they just dye it red and the darker areas of the figure turn, well, darker red. The level of black that they get in a colored finish is pretty incredible. For something like the bengal burst, they dye with black or brown, sand back and dye again with amber. Then during the finishing process they add a burst around the edges. How much of either of the dyes they use in the process is something for debate. Also how strong the dyes are when they dye any of the colors is another secret we probably will not get out of the Warmoth Finishing dept. I have some more dyes on order and some test pieces to try when ever I get everything. One last thing, the wood before it is finished will not appear the same, obviously. They use the wet look on the site for pictures for a reason.
Patrick