You can have a lot of fun with your idea….I think you need two constants in your scheme if you can see one room to the other. I suggest each sofa be white and slipcovered. For instance: Yellow room:Lavender room: The other constant: similar rugs. A white bordered sisal rug, for example

I love monochromatic spaces so love to mix shades of neutrals! I think it will be beautiful and soothing together...I think your wall color may be to yellow...that might be something that needs to be changed...or it could just be the light? What color are the walls?

There is no rule about this, but more often than not they are the same color.

What about a medium warm grey, which would work well with walls, fireplace and hopefully your chairs (not sure if they are the same color). Add warm toned textured cushions. (I wouldn't use dark brown as the two chairs are already dark enough in room.) You had asked for overall ideas for room, hope some of these help. Given you have centered couch to fireplace, it is off centre on wall. What do you think of a couch or sectional in front of window with a table/lamp on one end and a floor lamp on the other. This will also help fill the empty corner near fireplace On the wall as you enter, add a console and art Place your two chairs facing window. Adding a mantle would be great Linen like drapes (@Ikea) would warm up the space I’d change the art over the table next to fireplace and add pottery on the table Add a large basket on the floor next to fireplace. I have the one below and it’s large and well made