I'm no expert on dress regs but... I work out in the states and we wear Khaki Dress (not sure what number 4?) during the summer months and blues in the winter. We're issued stone coloured short and long sleeved shirts and short and long trousers and browny green suede shoes. The embassy inform us when the switch beween winter/summer happens. We are also issued No 6 dress, equivalents to No 1s but in stone colour. We're also issued No 8s which is mess dress, white jacket with shoulder boards and blue trousers. All said, wherever you're going, you'll be entitled to whatever uniform is officially worn at that location. You can't just wear the uniform of your choice, even if it is official uniform!