Cleaning an old embroidery

by Helen
(Queensland Australia)

Hi, attached is a picture of a beautifully embroidered picture we bought from an old lady. The embroidery is lovely, but it is embroidered on very fine cotton or something, which is quite discoloured in the pathway and sky. It was once white, I think, and is now patchy brown. Any ideas on how to clean the middle of it without touching the flowers, and what to use?