Bigger is better. This is to include caps, etc. Changes whole character of room. Sofas and side chairs. No patterns here.
Any solid color is considered neutral.
It can be purple as long as it is not a pattern. Textured patterns are fine. Just not a variation in colors. Doing this will help your furniture endure the test of time. Pillows, small upholstered ottomans and drapery and area rugs.