Ashish, The workmanship seems to be an issue with your stone cladding wall. Interlock joints are visible and dirty. This needs to be thoroughly cleaned and grey cement will need color touch ups. Some people go for a lacquer polish to enhance the look of the stones. However, it is equally repulsive for some people who like natural finish. Get a sample stone done first and then decide for the entire wall. It appears to be sandstone, hence it is better if it is coated with lacquer. Thanks, Nitin CORNERSTONE DESIGNS, Bangalore

Siraj, sharing few pics would help the imagination.

Can anyone please tell the colour of wall paint?

Either, you can paint all the walls with light grey or white colour. Or, highlight one wall with light grey colour and rest of the walls can be white.