JWST wavelength sensing starts at 600nm, corresponding to red/orange visible light, and then into the IR. It seems there is no sensor or filter included below 600nm meaning that green and blue light cannot be imaged at all, meaning all images must have to be displayed as false color composites. The mirror surface is gold which reflects well (>90%) above 600nm and falls off to around 35% - 40% at 400nm. This seems to be the justification for not including any blue or green sensing, even though gold still reflects 35% of 450nm blue light and 70% of 540nm green light (ref https://www.inradoptics.com/capabilities/coating/spectral-reflectivity-curves).
So a blue and green filter could easily have been fitted - their image gains increased electronically to compensate for the gold spectral response (the lower SNR would not be a problem for the very bright outer solar system planets). This means, very disappointingly, that when the outer solar system planets are imaged, we will not get real color images but false color instead. Very disappointing and a major oversight in my view. When the next event happens on Jupiter or Saturn we cannot get real color images of it from JWST, for the sake of two cheap and lightweight dichroic filters.