Yesterday I bought a strange looking fantail goldfish. He has a yellow-silver color that I've never seen before in a goldfish. Also he has a brown spot on top of his head. This fish is very young, about 1". I was wondering if he might change colors because I don't recall seeing any pictures...
You've got to be kidding. All those fish in a 4-foot long tank? You'd be luck to take care of 4 goldfish long term in a tank that size. You need a 40-foot long tank to try all the species shown in the pictures.
Three goldfish are too many for 24 liters. You should try to keep only one in that tank if you want to improve your chances. What type of filter do you have? Goldfish are very messy and typically require more filteration than tropicals.