You'll need two things to start solving this puzzle; one is in the cellar, and the other is in the cemetery.
In the cellar, look closely at the wine rack on the right as you enter. In an empty slot at the bottom right, pick up a small handful of blue and green tiles.
Go find Beauregard's headstone (it's in the first row at the left as you enter the cemetery) and wipe the dirt off the bottom. If you've solved the crypt window puzzle, you'll see a row of colored tiles; take a picture of them with Nancy's camera.
Go back up to Charlotte's bedroom and add the tiles to the jewelry box, and you're finally ready to solve the puzzle (sigh). Read to the end of this hint for the solution.
The basic goal here, as Nancy says when you add the tiles, is to click on the tiles to trace a line from the top left corner (starting with the one tile that's kind of lit up) to the top right corner. See the tiny arrows outside the tiles? They show the start and finish of the path.
The trick is that you have to click on the tiles in the same order of colors that you found on the bottom of Beauregard's headstone.
So if you're playing as an Amateur, Beauregard's headstone showed purple, dark green, dark blue, and light blue tiles. The first tile at the upper left is purple, so the next tile you click on should be dark green.
There are two dark green tiles here, one to the right and one diagonally down to the right. Pick one, then look for a dark blue tile from there. See how it goes?
You can click on any tile that touches the last one you clicked on -- up, right, down, left, or diagonally -- as long as it follows that same color pattern. Once you've clicked on a tile, you can't use it again.
You don't have to cover anything like the entire square, but expect to wander all over the place before you finally reach the upper right square.
Totally frustrated and lost? Happens a lot, partly because Nancy doesn't tell you when you go wrong until you've gone a long way. There may be other paths, but here are the ones that worked for me:
Inside the little drawer that popped open, there is an odd note about the clocks.