The color channel's effect on the dose-response of Gafchromic™ EBT2 and EBT3 radiochromic films irradiated with a 6 MeV electron beam in the range from 0 to 1000 cGy was investigated and compared. A Canon flatbed scanner was used to scan the irradiated Gafchromic™ EBT2 and EBT3 films, while ultraviolet-visible (UV-Vis) absorption spectra were analyzed with a spectrophotometer. Triple RGB channel, weighted and unweighted grey images were analyzed using the free software ImageJ. As the 6 MeV electron beam dose increases, the pixel values of the red, green, weighted, and unweighted grey images decrease exponentially for both Gafchromic™ EBT2 and EBT3 films. The blue channel fluctuates with the increase of 6 MeV electron beam dose for both EBT2 and EBT3 films and decreases the unweighted grey image more than the weighted greyscale image. The characteristic peaks at 582 ± 2 nm and 632 ± 2 nm of Gafchromic™ EBT2 and EBT3 films are correlated with the absorbed 6 MeV electron beam dose. The sensitivity deterioration constant b3 (is a free parameter of fitting in units of (cGy−1)) of EBT2 film is higher than EBT3 at both characteristic peaks at 582 ± 2 nm, and 632 ± 2 nm, indicating that EBT2 has better sensitivity at the expense of dynamic range, whilst EBT3 has lower sensitivity but a higher dynamic range. In comparison to the red and green channels, UV-Vis absorption in the blue channel range between 450 nm and 490 nm has a weak response and a small dynamic range. The Gafchromic™ EBT2 and EBT3 films scan with monochromatic red or green channels resulting in increased sensitivity and a wider dynamic range.