Hi Mick,
I don't know the answer, but you may find my experience helpful.
I bought some Ludwigia Repens "Rubin" (red) from ebay. They arrived nice and red, then a week after planting they were all bright green. After doing a bit of research, lots of people will tell you to dose 'Flourish Iron' or some other equivalent product. This had zero impact on my plants after 3 months of dosing. I stopped dosing at this point. This isn't to say that 'Flourish Iron' wasn't doing it's job, but I believe another factor may have stopped it from working.
I've have had all sorts of Algae issues with my tank which I've recently found out to be because my lighting intensity was way too high. Now that I've turned the intensity down from 50% to 20%, even though I'm not dosing Iron any more, I can see the plants slowly changing colour again.
I haven't started dosing Iron yet, I want my tank to recover from it's uyalgae issues before I start messing with the water chemistry, but I think having high light can turn your plants from red to green, so it could be that your plants are half way between, coming out slightly brown. You may find that turning the light intensity down (not the length of time the lights are on for) will help bring out the red a bit more, but this idea is purely hypothetical, given my experience and results.