You are right, – its most often the males that are shown in the photos, – but we will try and make this better.
There are a few photoes of females in the species sections (nagyi, linkei and filamentous)
There are two photoes of filamentosus female, so maybe that can help you ?
Generally in young age it is really difficult to tell the difference between sexes. Both male and female with most species have the same neutral colouring of black and white stripes along the body. Only males have additional colour bands in the different fins, – again depending on the species. Once they are adult and coloured up, you are not in doubt, but before that it can be really difficult.
To me its a question of rather a long experience which sometimes makes me think I can determine whether its male or female by the shape of the body, but 🙂 .. not really 100 procent. Some species are easier than other, f.inst. I find that P.parvulus shows differences from quite early, whereas species such as P.nagyi and P.harveyi looks the same untill you start being able to see the colour band in the tail, – this you only see with the males.
The best way I think often is to provide good conditions for the fishes, add caves to the tank. This will make the fish colour up, and then you might be able to see what is what. However of course, more males in a tank, might make subdominant males look ‘female’ almost, but most often you will – depending on the species – be able to see a little bit of the colour marking in the tail fin.
A male without a female in the tank – will probably never really show deep colours. He might show some aggression colour, but this will be less ‘sparkling’. A male will react to a female by being interested and ‘tolerant’ 🙂 and charming 🙂