Although there have been a lot of products sold at similar prices, the 1999.99 RMB (327.05 USD) OnePlus One is still one of the best products that are worth the price.
Regarding the rear cover, the OnePlus One only comes in sandstone black, and baby skin white as of now. There is also a bamboo version. Netizen @palm, however, has leaked photos that show a yellow OnePlus One rear cover, but nobody knows what it is made of.
Of course, as of now, there is no way to confirm whether this is an official rear cover by OnePlus or a 3rd party product. Hopefully, it will have a comfortable texture.