Practical, loyal, weathered folks. Settled nomads in ths North.
I have started this project thinking that orcs can't be impossible to dress from the high street - but it'll be hard. Battered armour, military stylings, robes and a warskirt are more or less the core Orc look, plus wristwraps and a scarf. There's no particular rules as to colours - your in-game group may have a colour scheme that will be tied into their group purpose and/or their original tribe or where they were raised.
You could make a basic Imperial Orc with any other nation's kit, weathered and scuffed up, put some wraps and a mask on and call it job done - but we'll try and find some uniquely orcish pieces.
Brown, Mud, Rust, Metal, Leather, Bright Accents
Imperial Orc gear looks worn, well-loved and uses lots of layers. Faded colours and visible repairs are great. You also want as much skin covered as possible, so you don't have to worry about makeup if your orc has a different skin tone to your natural skin.