In the zebra"sh retina, four types of cone photoreceptor cells (or cones) with di!erent sensitive frequencies are arranged in a regular pattern, named &&cone mosaic''. A pair of small cones, one sensitive to red and the other sensitive to green, is in close contact and forms a &&double cone''. In addition, there are two kinds of single cones, sensitive to blue and to UV, respectively. We study characteristics of cell-di!erentiation rules that realize stable formation of cone mosaic. Assumptions are: undi!erentiated cells are arranged in a regular square lattice, and they are one of the three types (B, U, and D cells). A D cell has two parts (G and R-parts) and takes one of the four directions. The cells change their cell type and orientation following a continuoustime Markovian chain. The state transtion occurs faster if it increases the stabilities of the focal cell, in which the stability is the sum of a$nities with neighboring cells. After the transient period, the system may reach a stable pattern (pre-pattern). The pattern becomes "xed later when the cells are fully di!erentiated in which B cells, U cells, and D cells become bluesensitive, UV-sensitive, and double cones, respectively. We search for the combinations of a$nities between cell states that can generate the same cone mosaic patterns as in zerbra"sh retina. Successful transition rules give (1) zero or small a$nity with the pairs of cell states that are absent in the zebra"sh cone mosaic ( 30, % and the contact of two cells of the same type); (2) a large a$nity between a part of D cells and a non-D cell ( 3% and 0 ); and (3) a positive a$nity of an intermediate magnitude between two non-D cells ( 3) and between two parts of D cells ( %0). The latter should be of a magnitude of about 60}90% of the former. The time needed to form a regular pattern increases with the lattice size if all the cells start pre-pattern formation simultaneously. However, the convergence time is shortened considerably if the pre-pattern formation occurs only in a narrow band of morphogenetic cell layer that sweeps from one end of the lattice to the other.