Be careful with neutral wall colors and do not go too "COOL", as the drapes have warm tones. If you can take one down temporarily, or have a piece of fabric from them, go to your local Benjamin Moore or Sherwin Williams store. They can assist you in finding a neutral with warm undertones to compliment the drapes. Get samples and some poster board. Put two coats of sample paint colors on each board, not on the walls themselves. (The current paint changes the sample color) Then you can move the board around to different spaces and try the paint in different lighting.

A warm white on the walls. I would also lighten the ceiling. Use the same color as the walls, or one or two shades deeper.