Only a quarter of the world's capitals don't contain the letter A! Firstly, hit any key, which will show all world capitals except the ones that do not contain the letter A. Then, name those capitals that have no A in them.
Colombo is named as the capital by many publications, including Encyclopedia Britannica, Lonely Planet, Wikipedia, plus several websites like this one. Sri Jayawardenapura Kotte is a suburb of Colombo, about 9 km / 5 miles from downtown. I use both answers as capitals in my quizzes, because that aligns best with reality!