Why GREEN light is recommended for these products?

All lenses operating in the visible range, including OE Telecentric lenses, are achromatized through the whole VIS spectrum. However, parameters related to the lens distortion and telecentricity are typically optimized for the wavelengths at the centre of the VIS range, that is green light. Moreover, the resolution tends to be better in the green light range, where the achromatization is almost perfect.

"Green" is also better than "Red" because a shorter wavelength range increases the diffraction limit of the lens and the maximum achievable resolution.