I don't remember Ridax selling a red version, but his module could work with various LED modules. One of the advantages of the Penta 3 is that the display circuit outputs a serial data line to a universal LED module. By universal I mean if you were to somehow turn on all the segments of a Penta 3 display, you'd just see a big grid of little dots - there's nothing custom about it. This means that in theory, you could replace just the LED display with another serial input display of the same size and it should work. So I imagine it wouldn't be too hard to find a red one.
The Penta 1 and 2's use a parallel display interface with a custom LED display. Custom meaning if you were to turn on all the segments at once you'd see whole words such as "CD", "AUX", etc, not just individual pixels. That means you can't replace just the LED module, because a universal one wouldn't know how to interpret the inputs. To replace the display, you'd have to also replace the electronics for decoding the display signal. Ridax's modules included that, which is why they worked in any Penta.
Mind you I haven't actually tried this. It's only what I surmised by looking at the circuit schematics in the service manual, so I could be wrong.
Either way it's an interesting mod, can you tell us anything more about it?