Its amazing how dis-coloured cave walls can become, especially if your running an open fire or wood burning stove. Caves are predominantly painted white on the interior to enhance the natural light which generally comes from doors and windows at the front.
The type of paint to use internally can be an issue - it depends who you talk to.
For us, plastic paint has been the way to go. Practicality wise it does not leave a residue unlike "Cal" which has been used in old Spanish buildings for years now, however the paint is not "breathable" so ultimately its is a matter of personal choice. Our cave has been painted with plastic paint for over 4 years with no detrimental effect.
A 25ltr tub of paint will cost in the region of 25 euros, how far will that go? Well it can be watered down slightly but we painted two rooms - surface area approx 120m2
Not a bad deal and what a difference!