"Ah, one of the deluxe models. Come to save us with your 'superior' training?" 
"This 'deluxe model' is the only thing standing between you and a bloody death. So you best be showing some respect, trooper." 
"Y-yes sir! W-what are your orders, sir?" 
―Anonymous clone soldier and RC-1138 "Boss" aboard the Prosecutor 

The republic commandos were some of the Galactic Republic's most elite clone soldiers. Bred with less alterations from Jango Fett's DNA, they were capable of more independence than their more common brethren. The commandos were specially trained by around 100 elite trainers, of which 75 were mandalorians. 

This is the standard Katarn-class armor worn by commandos, though some squads, like the Delta squad, choose to customize their armors with paint to distinguish each other. One squad who didn't alter their armor esthethicly was Omega, who are the main protagonists in the book series Republic Commando.

When the Republic was replaced with the Empire, though, the commandos' armor went through some changes, most notably that it was recoloured to black.