If it's a dedicated room, then ideally paint it black
and cover the front part of the room's ceiling and walls in black velvet like 'Devore'. It's the first metre or so that makes the most difference, even if the rest of the room is quite light colours it would help.
If this is too severe, then dark grey, plus front velvet would be pretty good and much better than light magnolia and a white ceiling. More neutral colours are better incase some of the colour cast gets bounced back to the screen, but you'd probably get away with purple if you have the velvet for the front part. IMHO the skirting should be painted a dark colour as well otherwise it stands out like a sore thumb and probably would be distracting when watching a film in the dark as it will light up due to the reflections off the screen.
I'd have loved to have a dedicated room when I had my projector setup, but I did experiment with putting up a black cloth 'tent' (which simulates the dark walls you're talking about) and it made a huge difference to the picture, especially on brighter scenes. Best of luck with the project.
EDIT: Just to add that this is if you are trying to maximise the image quality of the setup: Dark paint, trim and no reflective surfaces (ie pictures) in front of the viewing seat to distract or reflect light back to the screen. Ideally you should also dress head to toe in black.
If you want it to look nicer with the lights on for some reason, then allow for some compromise, but it's a dedicated room at the end of the day not a living room...
