Listen to Predator soundtrack.
Forgetting how good this was and how similar it was to Aliens soundtrack by James Horner
Also notice earlier Jerry Goldsmith weird horns influence.
(Then notice other things... How close Jurassic Park Lost World score is to parts of this and elements from Holst's The Planets.)
Oh and use of freehand airbrush on Wacom Cintiq, pressure 14, one colour selected: RGB 117, 143, 150. Then throw in a bit of background and colour/level adjusts.