I have a Red Rubin Rosettta.

It was always a dark maroon, and in the last 9 months barely grew.

Then this week I pumped Co2 into the tank via a Nutrafin CO2 unit.

This week an entire leaf grew (a 5 incher) and it is red-as-day. Not
maroon like the rest.

Get CO2 if you don't already.

On a side note, someone was asking about a great red center-piece
plant is. My Red Rubin Rosetta is easily the eye catcher of the 10G
tank.