Disclosed is number coding of pairs (“doublets”) or small sets (“multiplets”) of solid phase carriers which provides distinguishable subtypes of a given type of such carriers, where each carrier type is distinguishable on the basis of a different code. Such number coding is useful for augmenting a coding system, such as a color code, and thereby effectively multiplying the number of “colors” (distinguishable sub-types). It can be applied, for example, to determine whether a sample is homozygous or heterozygous at a number of different sites for one of two different alleles, where the same color code is applied for each of the two alleles, and the alleles with the same color code are distinguished by knowing how many carriers are associated with molecules which detect each different allele.