Lime Wash Resource
Lime plasters and lime wash are a great finish for earthen buildings, stone, and other porous materials. It has been used traditionally on cob structures of old, maintaining a durable finish. A lime wash can fill hair line cracks in a earthen or lime plaster as well as act as a sacrificial protection layer. Lime wash can be made with just slaked lime and water.
I have a limewash in my bedroom and find it to be ultra bright white. Pigments can be added to change the color. The trick with a wash is several thin successive coats.
Sarah Jackson, NCPTT architectural conservator, has created a great resource for learning about lime.