I understand that hairspray will do it. Put a pad of white rag or kitchen paper on the top of the stain and blast it from the back with hairspray....next question, how to get hairspray out of combat trousers??
You can also get a biro stain remover from the supermarket
Our daughters both use Dylon Fabric Care StainRemovers. There are 3 different types, but they use Stain remover 1 (in a blue bottle) & Stain Remover 2 (in a red bottle). They both remove the different stains their children create & are very pleased with the results!
I swear by neat washing up liquid - ' Fairy Liquid' is my chosen brand. Squeeze a generous amount on the area of the stain and wash immediately at normal temperature! Works for me!! Good Luck