Red leaf plants are red because they reflect red light. Since red light is the primary light to drive photosynthesis (along with blue but red is the more important) the tanklighting generally has to be more intense for red plants, which is one reason they melt away so often. And with more intense lighting, CO2 becomes a possible issue.
There is a species of crypt, Cryptocoryne undulata, that is brownish-red; I had this years ago and it did well without the brighter light, and it does provide some contrast.The lanceolate crinkled leaves of this species may be chocolate brown, olive green, or reddish-brown on the upper-side and a rosy copper on the underside. A height of six inches makes this a beautiful contrasting plant in the fore- to mid-ground of the aquarium.
The floating plants like duckweed and Salvinia will obstruct light less than the more substantial plants, though you lose the nice submerged root effect which fish love to browse for food. Some stem plants left floating can work too, and it is easy to thin them oout regularly.
