Cut and sanded wooden blocks
Lay out your cookie sheet with drying rack. Cut the top off of your food coloring container.
Step 1: Cut and Sand Blocks
Once cut, sand them with medium grit sandpaper. I used an electric hand sander for speed. Be sure to knock down the edges, corners, and any other potentially splintery areas.
I made about 50 blocks. 12 or so for each of the 4 colors.
Step 2: Color the Blocks
I used food coloring added to some water to dye the blocks. My ratio of coloring to water is about 7:60. That is, each food coloring bottle was 7ml, and I added that to 60ml (1/4 cup) of water. This produced a medium tone, still allowing the wood grain to show through a bit. I wouldn't go any thinner, but if you wanted darker, especially for a light color like yellow, use twice as much food coloring.
Dip them into a dish with the food coloring in it, kinda like coloring eggs. Depending on the wood, let them soak for about 20-30 seconds. You'll know they've soaked enough when you see the coloring start wicking up the sides. Rotate the block as necessary to color each side.
Set the blocks on some sort of rack for drying. I made a rack out of skewers on a cookie sheet. Try not to use paper towels as the towel will soak and steal your dye from the block! They should dry virtually identical color to the colored toothpicks.
For larger blocks, use a dish that just fits the longest edge. The key to a good dish is one that is very flat on the inside bottom. A bowl may not work, but a flat plate or serving dish.
The amount of coloring should cover about 15-20 blocks, depending on the block size and how long you soak them.
Again, depending on the wood, the dye process might not be perfectly even. You can either enjoy this random variety or soak the pieces again or longer.
Do your lighter colors first, and/or be sure to wash out your dipping containers to prevent color mixing/bleeding.
I'll be making another batch of round and triangle blocks, for which I'll mix some colors to make purple, orange, etc.
Step 3: Seal the Blocks
Once the blocks are completely dry, use light coats of spray polyurethane to coat and seal the blocks. 4-5 light coats is better than 2-3 heavy coats. Lighter coats should be smoother and you won't need to sand them. But if they are a smidge rough, use a very fine "wet" style sandpaper to smooth them out, or rub each side with a same-colored block and that should smooth them back out.