The national flag of the Commonwealth of The Bahamas consists of a black triangle situated at the hoist with three horizontal bands: aquamarine, gold and aquamarine. (Source: Wikipedia)
You need:
- A loom (2 string and 2 planks)
 - Cyan banners (6x Cyan wool + a stick)
 - 2x Yellow Dye
 - 2x Black Dye
 - 1x Shield (6 planks + 1 Iron Ingot) (Bedrock Edition from Tails and Trails update)
 
How to make it:
- Make a loom. Put two strings and two planks together in the crafting table.
 - Make Cyan banners using one stick and six Cyan wool in the crafting table.
 - Bring the Cyan banner into the loom.
 - Add yellow dye and pick the Pale design. Do this twice.
 - Add black dye and pick the Inverted Chevron design. Do this twice as well.
 
That’s the finished Bahamas flag as a banner all done! So now we want to put the Bahamian banner on our shield, but first we want a couple more of these banners so we can decorate the village with them.
- Put the finished Bahamian banner in the crafting table. Add more cyan banners next to it. That’s how you copy or duplicate the banners.
 - Now put one of these Bahamian banners next to a shield in the crafting table and now you have a Bahamian shield! This also works in Bedrock edition from the Tails and Trails update!