I have a lot of red plants in my no tech tanks and they do much better than I thought they would. Light seems to be a big factor, both with color and leaf retention. Root tabs seem to help deepen the overall plant color, but not the colors at the top. I think iron tabs help, but I use them with total tabs and haven't withdrawn each for a month or so to see what happens.
The first pic is a 29 gal and the repens in the center shows the color fade from deep red near the top to green lower and then no leaves near the bottom. Light is 6700 t5's, four NO tubes. The pic somehow made the ludwigia look paper thin, but it's very healthy, in the month since the pic was taken, the plant has grown across the top of the tank and is a very intense dark red. No ferts in here at all, no CO2.
Second pic is a 45 gal with AR in the back right corner. The color change toward the bottom is apparent here. That clump was getting total and iron ferts and the colors were deeper, but no ferts for maybe 2 months in this pic. Again, no CO2, one HO 6700 t5 tube, one HO t5 pink plant tube and two NO 6700 t5's.
Both these pics are close to what the plants really look like from a lighting standpoint, the angels are blue platinum veils. I can't really complain, stuff grows well enough for us.