hi! here are a whole bunch of related posts which may shed some light on colour conventions for flags:

Why do so many countries use the colors red, white, and blue for their flags?

Why are red, white and blue common national colors?

Why did countries in the British Empire like Canada, British India, and the Union of South Africa have red British ensign flags as opposed to the blue ensign flags of Australia and New Zealand?

Why did the American Flag retain the red, white, and blue of the Union Jack?

After the fall of the U.S.S.R., why did Russia choose a red, white, and blue flag?

Why does Malaysia's flag look similar to USA's flag? Is there some sort of code for national flag designing?

Why is Communism "red"?

What is the historical significance of the repeated use of the colours of green, white, and black on national flags in the Middle East?

Why are so many national flags so similar?

Why do countries in certain regions have the same colours in their flags?

Is there a historical reason that certain colours/colour combinations seem to appear again and again in national flag designs?