Single crystals of colloidal silica spheres, 110 +/- 4.5 nm in diameter, are visually observed in suspensions of purely alcoholic organic solvents, i.e., methyl alcohol, ethyl alcohol, and ethylene glycol and in their aqueous mixtures in the exhaustively deionized conditions. Single crystals appear also for aqueous mixtures of propyl alcohol and n-butyl alcohol. Close-up color photographs of the single crystals are taken. Two kinds of colloidal single crystals, i.e., blocklike crystal grow up from the homogeneous nucleation mechanisms in the bulk phase for from the cell wall and the pillar-like ones from the heterogeneous nucleation mechanism along the cell wall, are observable in these solvent systems clearly. The size of the single crystals increases significantly as the sphere concentration decreases, and the largest crystals appear at sphere concentrations slightly higher than the critical concentration of melting (phi(c) in volume fraction). phi(c) values are around 0.0002 in pure water and increase sharply as the fraction of organic solvent increases. The phi(c) values in 100% of methyl alcohol, ethyl alcohol, and ethylene glycol range from 0.01 to 0.02, which are substantially low compared with the reference values reported hitherto. The change in phi(c) is explained well with the change in the dielectric constants of the solvent mixtures. The important role of the expanded Debye-screening length around spheres and the intersphere repulsion is supported strongly.