Please post more of the room. Right now the only color I see in there is mustard/maize chair? the rest, gray, white, black are all neutrals. If you like yellow that would be lovely with the gray walls.

I would mount curtain hardware close to the ceiling. Make sure the curtains are the correct size and stop just before they touch the floor...the white ones you have are too short for the space and look a little like high water pants. Take down the picture over the window/door.

If you don't like yellow.... literally any other color would work with the gray, white, black neutrals.

What is that??? Is there even a window behind it?

Whatever you choose, avoid the skimpy look, which is what you have in your picture. The curtain should be about 2 1/2 times the width of the window -- 2 times will do, but not less than that.

It looks as though that is a religious picture? Let's see the rest of the room so that we can find the right place for it; squashed up againsr the ceiling doesn't look good.

wall color is not the "pop" in a room. it is the background that makes the furniture and textiles work, without pictures of the entire room & its use anything goes: blue, yellow, white etc