The restriction on white light source and colour filter in a colour joint transform correlator (CJTC) is discussed. Based on this discussion, a new method of channeling using a three-color grating for pattern encoding is suggested. It is concluded from the experimental result that, by using this new method, not only the restriction on the experimental condition is relieved, but also the power spectra of the encoded pattern are easy for experimental processing in parallel channeling. Besides, the zero order power spectrum forms an important channel for the shape-only correlation.