Red leaves plants tend to be on the higher plant care level.
Meaning red plants usually requires high light intensity, fertilisers and sometimes C02, depending on plant species like most rotalas but be aware some rotalas may still not turn red even under intense lighting, there may be other factors that helps these types of plants thrive.
It’s very much a trail and error in finding the right balance of light, ferts and perhaps co2 to bring out the red pigments of your plant leaves.
There’s no real one answers fits all.
But first step I would take is look at the care requirement for your specific plants and see what level of lighting you currently have and take it from there.
As above for bright reds you normally need high lighting, that then also means CO2 and ferts most of the time. Once you have them you will probably need to dose additional iron (and imo is the only time you need to dose iron).
Red plants are generally at the very top of the "difficult" spectrum for this reason.
I concur with members who put the light as the primary factor. I'll explain, as I've no idea how much of this will be new.
First, white light is composed of colours; you can se this when light shines through a prism, or in a rainbow. Aquatic plants need red and blue light to photosynthesize, and of these red is the more relevant. All blue light for example will not drive photosynthesis. Adding green to the red and blue improves plant growth. Plants appear green to us because they are reflecting a lot of this green light.
Red leaf plants appear red because they reflect red light. Since this red light is also key to photosynthesis (which is the growth) red plants need much more red light. Intensity is the key, so that means more intense/stronger light.
With stronger light comes the need for more nutrients to balance. Adding more fertilizer provides some of his, except for CO2. In most fish tanks the CO2 produced by respiration (fish, plants, and some bacteria) and primarily by the breakdown of organic matter in the substrate, will be sufficient for low and medium light plants. But the higher light increases photosynthesis which needs more CO2 and other nutrients. Finding the balance without going high-tech (with diffused CO2) takes some effort. I would also note that diffused CO2 is now believed to have detrimental effects on fish, so one has to be careful. Actually, the increased light is not good for fish either.
Agreed, what we have to remember is that fish do not have eyelids so they cannot diffuse light by themselves.
If one has light coloured substrate, the effect of the light is increased simply because this will bounce or reflect off the light substrate.
Increased light will stress fish out, and we all know stressed fish do not do so well health wise. So the addition of floating plants or shaded areas created by large leaves plants for example will be beneficial to reducing light in areas of the tank this will help create a more balanced tank.