silver?? are you sure it's a salvini? everyone i have ever seen has been yellow.
to get the best colour out of your fish feed a varied diet of pellets, fish and shrimp. also as stated above, keeping a pair will ensure bothe sexes will look their best most of the time
Salvinis have a yellow base. Females have more red and males have more green green. Yours is just young, give yours some time before you swap it out for another fish.