This item,Oneplus offers five version of their back cover: Black rock, Bamboo, Black apricot, Santos Rosewod and Kevlar.

Click image for larger version.  Name: covers.jpg  Views: 0  Size: 72.8 KB  ID: 22510

What's more surprising is that the phone system will have corresponding change while with different cover,monitoring on its own. We can check it as follows:

Click image for larger version.  Name: Black rock.jpg  Views: 0  Size: 28.6 KB  ID: 22511

Click image for larger version.  Name: Bamboo.jpg  Views: 0  Size: 30.2 KB  ID: 22512

Click image for larger version.  Name: BAC.jpg  Views: 0  Size: 29.2 KB  ID: 22513

Click image for larger version.  Name: santos rose wood.jpg  Views: 0  Size: 36.2 KB  ID: 22514

Click image for larger version.  Name: Kevlar.jpg  Views: 0  Size: 31.7 KB  ID: 22515

But the price for each version is uncertain now.