Hi Stefanie,
in my opinion, all your pictures show females. As far as my experience goes, females of some species can show this dark coloration (esp. the dominant ones) in the abscence of males.
Here’s a female of my bintan variant that your fish reminds me of:
If you had a male in your group, I think he would have to look like this, with all the females around:
…or like this:
You know whar I mean? …I think males can easily be identified by their strong contrast that females never show. …At least, if they are well acclimatized and in good condition.
Greetings,
Martin