Have you ever been in the Avenues and noticed the different types of clothing men wear? During the summer the 'thobe' (also called dishdasha and kandura) is usually white or light colors worn by Emirati and Omanis. I can spot the difference right away but I'm sure most expats really don't know there are so many differences.
We are used to seeing the Kuwaiti dress code as pictured below.
A white t-shirt and long cotton pants are worn underneath the national dress except for UAE and Oman, instead of cotton pants they wear a cloth wrap (wizar) under their attire.
This is information gathered through experience and some Google help, photos are from Google, if you have anything you would like to add let me know.