Please bare in mind that bits of this information is poor at best and sketchy at worst. Its not been easy to find said information, but we have worked with what we have got.
The interior cab lighting, this has been confirmed to be red. The GT3 when it was alive and kicking did have red cab lighting.
Lighting while engine is moving backwards - The GT3 does have directional lighting (and this is now fixed on the 2nd run), but the GT3 never ran backwards. It never had that ability to do so, it only ever moved forwards. At the time, we had no data to confirm or deny that the GT3 had directional lighting, nor was it easy to find any such information at all.
Lighting while engine is moving forward - The headcodes lights are meant to be white, obviously. The lights underneath the headcodes currently are white, while the lights on the tender buffer beam is red. We haven't found any information informing us otherwise. If any concrete documentation does come out confirming that they are in fact meant to be red, then we will happily correct our mistake.
If you have any questions regarding the matter, feel free to ask them and i'll do my best so answer them. - Michael