Colloidal crystals of mono dispersed polystyrene spheres in aqueous solvent were formed by a new drop-slide method. The optical properties of the CCA (Colloidal Crystal Array) were characterized by reflection spectroscopy. The very strong intensity of reflectance was obtained by the new method. The maximum of the diffraction peak is highly symmetric and has a relatively narrow line width of about 52 nm at wet state of CCA. An in-situ real time investigation on the formation of the CCA was performed. The reflection maximum was found to be 566.4nm and it blue shifted to a minimum of 486.5 nm over the first drying phase and then shifted to 432.3nm upon reaching the stable state. The shifts of peak position were determined to be 4.13 nm / min at the first drying phase.