I just looked on The Heritage Store site to see if they mentioned this. I couldn't find anything. I did notice that the Castor Oil Clean product comes in the dark amber bottle but obviously not the actual Castor Oil. I did a Google search and read that castor oil can be stored at room temps for over a year with no problem.
We keep ours in our bathroom linen closet. It is dark in there and always room temperature.
Funny, I purchased the Castor Oil Clean product to help wash off the castor oil. However, as I usually leave it on overnight, it totally soaks into my body and there is nothing left to clean!