1. A composition or kit for differentially identifying cells in an instrument comprising: (a) a fluorescent dye capable of staining cells, which has a dye emission spectrum; (b) a first antibody that binds to an antigenic determinant that is differentially expressed on populations of blood cells, the antibody labeled with a fluorochrome having a first peak emission spectrum; and (c) an optional additional antibody that binds to a second antigenic determinant that is differentially expressed on populations of blood cells, the antibody labeled with the same fluorochrome or a different fluorochrome having a second peak emission spectrum; wherein at least two spectra selected from the group consisting of said dye emission spectrum of (a), said peak emission spectrum of (b) and said peak emission spectrum of (c) overlap, and wherein said overlap forms a spectral pattern that cannot be separated by optical or color compensation methods.