I know that the flag of Saudi Arabia isn't going to be too easy to colour in because I drew this flag rather painstakingly to get the details right! It is just a dark green background but the kids will have to be careful to leave the detail white.
Saudi Arabia Flag Colouring Page
Here's a colouring flag of Oman to print for the kids. The central and left section is a bright red, while the crest stays white and the bottom section is green.
Here is a colouring page of the Bahrain flag, ready to be coloured in with its striking red and white design.