I had to Google, so I assume you mean these guys:https://mmh7.ubi.com/en/factions/dungeon/creatures/assassin
The main colour scheme there seems to be black and dark purple, with a tiny few red bits and highlights in bronze/gold.
If I quickly bring up this image of a Kabalite Warrior.....
........I'll offer my advice.
I would statrt with a black undercoat.
For the non-armour parts of the main body, go black there. Keep them nice and black, and maybe give them a wash in a dark blue, or paint these areas in a dark blue or gray, and then give them a black wash (Nuln Oil would do). If you'd rather keep to a purple, go for Druchii Violet.
The armour scheme of the M&M7 is very dark, coming to purple in the highlights, so I would suggest keeping the armour black as well, and using a Fine Detail brush to highlight every line or armour. I'd suggest in Xereus Purple, and then use Genestealer Purple to on the very tips of spikes, or highest points of armour.
Make additional clothes such as the Warrior's belt loin cloth in red (may want to go for a dark red) so it doesn't stand out TOO much.
Additional elements such as the gear on their belt and the gun can be picked out in gold and silver.
I think that gives a decent approximation of the scheme for the M&M7 Dark Elves.
And you also manage to avoid blending, as you get the effect you want purely from highlights on black.