Salaks are diecious, so there are male and female selections. Certain varieties are self fruitful like bali.
I'd plant all the seeds and then slowly cull most of the males once they flower.
Manual pollination isn't required, the bugs and insects should do it. Also, it's not a good idea either as they are super thorny - there's stories of people losing their eyes.
Seed color shouldn't matter. Mature seeds from the wallichiana variety were light brown in color vs. some others like gula pasir being black. I'd plant them anyways.