Step 1: Parts
You will need:
-63 1x2 bricks
For 3 color: 21 of each color
For 2 color; 42 of one color, 21 of the other color
Attach 3 bricks as shown. Repeat this 20 more times for a total of 21 stacks.
Turn the top brick, as shown, on 3 of the sets of stacks.
Start attaching the stacks as shown. Continue adding stacks until there are 7 bricks in the top row.
Add another one of the stacks that has the top brick turned. After adding 6 more stacks attach another stack with a turned piece. Finally, attach the rest of the stacks as normal.