Cactus green dye can not be crafted it is not shown with the other dyes in the crafting table.
This affects xbox and the windows 10 version of the game.
MCPE-29869
Cactus Green dye has been removed from the game
Resolved
Works As Intended
0
In order to get cactus green you must smelt cactus in a furnace with any fuel
https://minecraft.gamepedia.com/Cactus_Green