61 years ago, August 6 1962, Jamaica gained independence under this flag. It is the only national flag in the world without either blue, red or white.

This was an initial proposal, with the same colors in a slightly boring horizontal triband:

Another proposal rearranged it a bit, but was discarded as too similar to the flag of Tanganyika, which seems quite reasonable, since they did not know that problem would be short-lived:

In the end they went for the saltire, which seems like a great choice, creating a more unique and interesting design.

Wikipedia page about the flag