I wish I could be more help. I don't have a croton, but I've read that they need really bright light. Your brightest window possible in the house. They can be slowly introduced to outside sunlight, but direct sun outside can fade the color. If they don't get good enough light, they might lose the red coloring.
Crotons should be watered as soon as the soil is dry down the length of a fingertip. They're somewhat spider mite prone. I don't know anything about fertilizer requirements or how fast they grow.
I hope that helps a bit. Maybe someone who's grown them will come along.