What about using a thin sheet of tinted acrylic ? You will need to experiment with different colors to get the right balance between brightness and contrast, but I think an orangish-tint will allow the neon-color to transmit, while attenuating the non-orange colors. Basically, a color filter.
I dont have one of those clocks, mainly because I like building my own, but the versatility of the display types is something you dont see anywhere else. That stubbornness has taken me years to get a rack full of unique clocks, and a lot of time and effort (not to mention money...). If I could have all my time and money back and replace it with an EleksTube, would I do it ? That's a question that will haunt me for years.