I dont come here often, so if this is against the rules i'll delete the thread.
I'm looking for a book I read in the late 90's, genre fiction fantasy.
The major points that stood out in the book were:
everyone is capable of magic, this magic allows them to create night-black materials, like housing and clothes, temporarily.
there is a rising amount of people being born with blue skin, these people are more aggressive and eventually migrate to form their own society and country
the two countries have a war, and it's established that using the black-magic burns out souls from the pool of reincarnation.
the blue people age rapidly, and the protag has to fight his son, who is a grown man and leading the blue empire, in a one on one duel in a ring of fire. the protag knows if he uses the magic to create a fireproof cloak it'll burn out his fathers? soul.
lots of the combat en masse is fought using the black magic to make tiny little obstructions in opponents bloodstreams, or to sever their limbs.
i've been trying to find this book for years, just not very hard, i guess.
i forgot to mention but the blue people are people born without souls.