Hey Koi-Angel
Males of this species tend to turn a dark brown with white or light yellow stripes. Females and sub-dominent males (males that live with other more dominent males) stay the golden color with dark brown stripes.
I'm going to give you some words of caution. They are not to scare you off, but more to keep you aware of what can happen.
Fish like Auratus are very aggressive. The fish I mentioned are two of the more aggressive species that would work. That does not mean that they won't fight, and that does not mean that a fish won't get inured or killed. You can do everything absolutely perfect and you will still find that aggression is a problem with fish like this - some people like these fish just because of this.
Here are some tips to help you out:
Try to add only fish of similar size. Since the current fish is already fully grown (and larger then usual if he is 5" long) then you will have a harder time finding tankmates, and you will probably pay more for them too. Keep an eye out in various websites for people selling of there fish, I find it a cheaper source for adult fish.
The less fish you stock, the more chances that one of them will become harassed to the point of illness or death. You will want at least 10 other fish in that tank to help distribute the aggression.
When it comes time to add fish to the new tank, do it all at once. In other words, don't add your Auratus to the tank until you get at least some of the other fish, that way he doesn't have a chance to establish territories before the others can.
Don't add more then one male of any of these species, this is certain death for the weaker males.
Always keep that 10 gallon ready, that way if you observe a certain fish getting beat up pretty badly you can remove it, nurse it back to health, and then find a new home for it.
If your daugher is young, and/or you do not want her to deal with fish injury and death, then I advise you to get some more docile species of fish to keep. Perhaps your daughter would feel better about that if you explained that it needs a really big tank that you can't provide? I don't know, I'm just speculating.
as Juanvaldez already mentioned, lots of rockwork is important. one cave per fish is not enough, try to offer as many caves, crevices and niches as you can by piling up rocks of different sizes and shapes.
I hope this helps somewhat.
