Hi,
Thanks for your great question. I can see your friend's concern with more brown in your living room, and in trying to use two browns in the space which can be tricky. Love the idea of a dark accent wall.

If you have a photo to add to your question, that would be great. Without seeing your brown furniture and the undertone in the color, I can suggest some neutrals that could really keep the balance in your living room (plus a few accent color ideas.) The colors I'm suggesting can be mixed and matched with neutral accent, according to your taste, what other colors you have in the room, and what looks good with your lighting.

With brown furniture, brown walls, and a dark accent wall, it's possible that the room could become unbalanced. I've also found that using dark colors in a room with many windows, can often make the walls "disappear" in the contrast from the light coming in the room. Be sure to sample any colors you're considering, to be sure that you get the right amount of light balance in your living room.

If you have more details about the flooring and trim color, or anything else you think I should know about the room, please reply and I can suggest more targeted colors.

Here are my initial ideas for your living room neutrals:

Benjamin Moore Skipping Stone CSP 170 http://www.myperfectcolor.com/en/color/378817_Benjamin-Moore-CSP-155-skipping-stone

Benjamin More Dulce de Leche CSP-250 http://www.myperfectcolor.com/en/color/378836_Benjamin-Moore-CSP-250-dulce-de-leche

Match of Color Life Faint Wind http://www.myperfectcolor.com/en/color/331009_ColorLife-CL-2942W-Faint-Wind

Benjamin Moore Revere Pewter HC-172 http://www.myperfectcolor.com/en/color/102897_Benjamin-Moore-HC-172-Revere-Pewter

Here are Accent Wall ideas:

Benjamin Moore Knoxville Gray http://www.myperfectcolor.com/en/color/5971_Benjamin-Moore-HC-160-Knoxville-Gray

Benjamin Moore Caponata AF-650 http://www.myperfectcolor.com/en/color/103550_Benjamin-Moore-AF-650-Caponata

Benjamin Moore Wasabi AF-430 http://www.myperfectcolor.com/en/color/103506_Benjamin-Moore-AF-430-Wasabi

Benjamin Moore Azores AF-495 http://www.myperfectcolor.com/en/color/103519_Benjamin-Moore-AF-495-Azores

Please let me know if you have more questions! Hope this helps,
Diana