Hygrophila polysperma
Sunset hygro
Sunset Hygro was a really attractive plant with shades of light yellow, light green, and light to medium pink. Sadly it's a cultivated form of H. polysperma which is classified as a noxious weed and I think it's pretty much illegal in the US. There are other variations of the plant and all of them are classified in the same way.
For more information about Sunset Hygro please see my June 2006 column for TFH's "The Planted Tank," called The Genus Hygrophila.