[Frigid Blue]

How can I tell which is which when they are about 3.5-4"? I just bought a female for my male Spilonotus Tanzania, but it seemed really silver compared to my other older 5.5" female, which is more of a bronze/tan colour. Since it spawned with my male red empress (which I am now selling), she has turned into a darker colour similiar to my proven spilonotus. Are females normally silver when they're young?

 

[noki]

Can't really tell from your description, but yes it is normal for juveniles of most Haps such as those to be silvery, then get duller when older.

Look at the face/ mouth? Look at the markings? Does the female have a broken horizontal line? Any sign of vertical barring?

 

[Frigid Blue]

She had a solid horizontal line like a Red Empress, but it has since broken up into 2 faded lines (half and half with space in the middle) I noticed my spilonotus has a yellowish dorsal tip, but the questionable female has a orange dorsal edge... again, it is beginning to lighten up a bit.