GNS as used in HS125 and BAe146 Avro RJ had a ‘Plasdec’ (spl?) panel facing, which was lit internally for the engraving, as were the buttons. The older displays used a small monochrome CRT.
I spent many years using these systems, and notwithstanding to previous comments, the navigation (RNAV) was very accurate in the DME/DME mode. Longer range accuracy depended on operator choice of sensor and installation.
There were variants for inshore coastal surveillance and Nav Aid checking tasks.
The small version had some of the best aspects of human interface - no bells and whistles. The later, market driven versions attempted to mimic larger FMS, but not very successfully. However, providing only one operating method was used (button or line select) it retain its commendable qualities for its time and price.