1. A 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 a first population of blood cells, the antibody labeled with a first 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 a second population of blood cells, the additional antibody labeled with a second fluorochrome having a second peak emission spectrum, wherein the second peak emission spectrum is the same as the first peak emission spectrum or different from the first peak emission spectrum; at least two spectra selected from the group consisting of said dye emission spectrum of (a), the first peak emission spectrum of (b) and the second peak emission spectrum of (c) overlap to form a spectral pattern that cannot be separated by optical or color compensation methods.