Depending how vivid your scarlet is: You can go with white or cream so it really is the accent wall and nothing is shouting for equal attention You can also go for a muted grey or beige

White, blue patterned, or even a bright accent color like red or yellow http://houzz.com/photos/10435177 http://houzz.com/photos/124382 http://houzz.com/photos/44046

What soft furnishings do you have. You could pic out one or two colours as an accent colour and use that as your Base for the curtains. I currently have cream hessian walls and have a duck egg blue and chocolate curtains. I'm currently making matching Oxford cushion covers for the settees . If you can't find what your looking for ready made buy the fabric and have bespoke curtains made for you.

The furniture in the 1st one is typically seen in renders and that's what gives it away. Also the tree is not quite real. Other details like creases in the carpets/dhurries and the pattern of it.