I had a tiger lotus in 1.2WPG but with HO T5's which give out more light and i had a big tank (40g) so i bascally had 2WPG almost. What are your lighting levels?
This answers your question. these are in a 0.9WPG T5HO tank (30W/33USG.) I think that answers the colour statement too. There are different colours of the plant so maybe you think the low light minimised the bright colours when in fact you have a different colour OR you have Nympheae Rubra which is often called Tiger Lotus but isn't. Nympheae Rubra has a more plain leave normally burgandy-ish. Zenkeri has distinctive burgandy flecks on the back ground colour as you se below:
Nympheae Zenkeri Red
Nympheae Zenkeri Green
Low light doesn't slow their growth either, this is produced by 1 red zenkeri bulb!!!!