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For rapid and accurate identification of graphenes by optical images, a total color difference (TCD) method is proposed and demonstrated based on a combination of reflection spectrum and International Commission on Illumination color space. The preferential thickness of different dielectric films covered on a Si substrate is well elucidated, and a 72 nm thick Al2O3 film is found to be much better than the commonly used SiO2 or Si3N4 films. The TCD both between monolayer graphene and substrate and between graphene of different layers (an be further improved by appropriately narrowing the wavelength range of the light source. Moreover, the influences of the objective lens in a real-world optical system on the TCD are also discussed. These findings provide useful information for rapid evaluation of the layer range of graphenes simply by different color bands and for accurate and reliable layer identification due to large TCD values, which opens up the possibility for the nondestructive identification and physical property measurements of graphene with an optical microscope.