I believe a light grey would look nice behind the blue in the map - it needs to be a perfect shade of grey as grey is hard to achieve. Possibly experiment with various colours - I usually paint on board using sample pots first then hold them up in large sheets to see what suits the area... This gives you an indication of where throws of light will capture the actual colour and which shades suite the room without having to paint on the walls. The board base colour generally needs to be as close to your existing wall colour to achieve the closest match.

Your walls could be alost any color as for the furniture I would look into the tapestry and when that is decided choose a color from it for the walls

what colour on walls if whole cupboard is of dark purple

Keep things cool Cooler shades such as grey and blue help walls recede, making the room feel more spacious and light. Bring home the sunshine Light but warm colours such as terracotta or yellow can mimic sunshine and make a space feel bright and airy. Pale ceilings Keep the ceilings in a light colour to make the room appear larger and lighter. While white is your safest bet, you can opt for mint or sage green for a pop of colour.