Roman blinds are usually mounted inside the window frame. They are made to completely cover the window without any light peeking through. Wall color will depend on what color your bedding is. You definitely want to go with a light color due to the dark carpet and small window, unless you like a dark bedroom. I sleep in the daytime and love having a dark bedroom but not everyone does.

For color, how about Sherwin Williams Sea Salt? I've seen it praised so much here on Houzz that I'm thinking about using it in my bedroom. As you can see from the pictures I've included, it reads almost as a different color depending on the light the room gets. So, you definitely want to try a sample first.

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P.S. I had an email from SW for a 30% coupon through April 1. So, don't forget to look for that if you decide to use SW.

I too love the Sea Salt color but you need to choose bedding first before wall color or roman blind fabric. It is such a small space that light colored bedding will cover up most of the dark carpet anyway