Why are the white "flowers" turning green.
This happens because the white structure that appears to be a flower petal is actually a type of leaf called a spathe. The actual flowers are tiny and found on the spike-shaped structure. Each spathe will go from white to green as it ages and reverts back to being a photosythetic leaf.
To prevent your plant from being full of green "flowers," you can cut off (deadhead) the flower spikes that have green spathes. This will encourage the plant to produce more flowers.