This post comes with a warning - There's really not much in it! I have struggled to find research on castor oil. I have heard it can do many things but this is not reflected in the science. I have been asked to comment on Haitian and Jamaican oil and the difference between refined or unrefined oil but I have to hold my hands up and say I have nothing.
What I did find about castor oil
1. Increases luster of hair (therefore likely not to penetrate hair) (J. Soc.Cosmetic Chemists, pg 335-351, 2003)
2. Low irritancy and unlikely to cause spots (J. Soc, Cosmetic Chemists, pg 321-333 , 1989)
3. Substances derived from castor oil can help moisturise bleached hair and aid with combing ( International Journal of Cosmetic Science, pg 169 - 190, 2007)
4.Castor oil used to dilute other compounds and is widely used to make lipsticks as the pigments can dissolve easily in castor oil (J. Soc.Cosmetic Chemists, pg 153-32, 1964 and Journal of the American Oil Chemists' Society, pg 406-408, 1972)
If you are hungry for more information, then I will send you over to BGLH where Jenteel has a lot more to say - Read it here