I have always considered staining of wood siding to be longer lasting and more durable then paint..........I am confused when you say that paint will last longer. Maybe you can do a little more research and find a stain that you are comfortable with that will last longer then paint and will give you the look that you want......It would be sad to cover up that lovely wood siding with paint.

The grey on the western wall looks dark and purplish on my monitor. It may come over as too imposing and monolithic on the southern face. If you're sticking with the grey palette then a warmer tone would suit the sandstone better. Does Dulux have a colour palette recommendation that includes your Berkshire White plus a grey? Check online or in store pamphlets. But, for such a big, expensive, and impactful paint job I would actually be tempted to get a colour consultant. You're not just repainting a loungeroom wall if it doesn't work!

I think painting the walls lighter and brighter is the right move but don't be restricted to white necessarily - although that would be the safe option and you know for sure it would work! You could introduce a contrasting colour on the ceiling if the walls were white obviously dependent on your furnishings and other colour choices. How about a soft grey or "greige" as an alternative to the white? Finally, you could introduce a dado rail at approx 1m from the floor - painted white the same as cornice and ceiling and then paint the upper and lower sections in contrasting colours of say charcoal on the base and white above or 2 shades of the same colour.

There are lots of paint manufacturers apart from Dulux, and hundreds of whites that it could be. Unfortunately the natural light in the photo, the type of camera, any photo editing, and the adjustments on your computer screen make it impossible for anybody to say with any accuracy what the colour may be. The only way to find the right white is to get samples and make your own judgement on site. I always think that Perth light seems stonger and brighter than Sydney light - possibly due to Sydney's airborne pollution in the inner city? There are lots of online resources by various paint manufacturers about choosing the right white, but don't make selections from an online digital image as it won't be accurate. Best of luck, Dr Retro of Dr Retro House Calls