Okay kiddo, so every country has special colours that they use to represent themselves. These colours are usually based on the history and culture of that country. In Ukraine, their national colours are blue and yellow.
The blue is for the sky and the many rivers and lakes in Ukraine, and the yellow represents the golden fields of wheat that grow there. These two colours together create a beautiful and unique symbol for Ukraine.
You may notice that the Ukrainian flag has two equal horizontal stripes - one blue and one yellow. This flag has been used for over 100 years and is a very important symbol for the people of Ukraine. They fly it proudly at events like sporting events and important national holidays.
So, that's the long and short of it, kiddo. Blue and yellow are the national colours of Ukraine because they represent the sky, rivers and lakes, and golden fields of wheat in the country. These colours are proudly displayed on the Ukrainian flag, which is a very special symbol for the people of Ukraine.