David, your fish are extremely interesting. But I doubt that they are P. sumatranus. At least in the male there is always a dark round spot to be seen (see other photos) which is very characteristic. The coclusive marker would be the position in the courtship: both partners stand upright 90 degrees on their tails, which is quite unusual with all Parosphromenus!
Therefore I do believe that your fish are not P. sumatranus. But which species are they? They look very much lime a species/variant that we only had once many years ago: P. spec. Palangan. As Fried Horst Linke told me some months ago all former habitats are destroyed over there. B ythe way, they were situated in Kalimantan, not on Sumatra. But of course, he could not visit them all. And additionally, in Parosphromenus there is always the possibility of a new form that we never saw before.
In any case, do inform us about further developments. Could you receive further sure informations about the origin of your fish?
Please, do write a personal mail to me.