Edge-to-edge contact between pieces of different colors, however, is allowed. Each new piece played must be placed so that it touches at least one piece of the same color, with only corner-to-corner contact allowed - edges cannot touch. The first piece played of each color is placed in one of the board's four corners.Order of play is based on the color of pieces: blue, yellow, red, green.The standard rules of play for all variations of the game are as follows: These shapes are the first in the A000105 sequence. The 21 shapes are based on free polyominoes of one to five squares (one monomino, one domino, two trominoes/triominoes, five tetrominoes, and 12 pentominoes). There are a total of 84 game tiles, organized into 21 shapes in each of four colors: blue, yellow, red, and green. The game is played on a square board divided into 20 rows and 20 columns, for a total of 400 squares. The shapes and values of the 21 Blokus tiles.