Hessen-Kassel provided the British fifteen regiments of infantry, each with five companies of men, four grenadier battalions and two companies of Jäger (known as chasseurs or sharpshooters in English).[8] The Jäger in particular were in high demand.[9] Jäger, a German word that translates to “hunter” and can be used as both a singular and plural word, were recruited from huntsmen and foresters who were skilled in the use of rifled weapons normally used to hunt boar.[10] They were skilled shots, self-sufficient in battle, and swift, able to efficiently load and fire a rifle, a skill which took greater dexterity than firing the muskets of the day. Most importantly, they were valiant.

https://allthingsliberty.com/2015/05/the-hessian-jagerkorps-in-new-york-and-pennsylvania-1776-1777/

The really short version is that blue coats indicated regular infantry armed with smoothbore muskets--your classic "let's stand in a couple of lines and shoot until one side gives up"--while the green coats were for skirmishers armed with rifles who acted as a screen, sharpshooters, etc.