We can combine blue and red to make purple, we can combine red and white to make pink... so why can't we combine blue and yellow to make green dye? Now you can!
Just download the right version, unzip the file, and pop it in your Minecraft > saves > [your world] > datapacks folder. Done!
You can even do this while you're playing! Open the world folder and put it in, then just run /reload and it should be good to go!