People living in warmer climates can still get the cold and flu viruses but people in warmer climates do get less colds and flues.
But the reason people tend to get less flu viruses and cold viruses in the warmer climate is because they're more exposed to sunlight which helps to improve and boost a persons immune system due to the Vitamins people get when exposed to the sun.
It's very important to get some sunlight to stay healthy and get plenty of Vitamin C which also helps boost your immune system.