Blue, red and purple are just a few of the colors you can paint the tree' leaves with dye in-game through this mod.
How do I paint leaves?
To turn the color of a leaf block into another you first need to get your hands on some dye. Dye is obtained differently based on what dye you want. As an example, Rose Red dye is produced from red flowers. Look at the Minecraft PE Wikia for more information about each dye.
Once you have got the dye simply touch a leaf block using the dye and it will shift color.