To answer your question, everything to the left of England will be blue and everything right of England will be green.
On a sphere (earth), the Prime Meridian run through Greenwich England (0° longitude). Everything from 0° longitude to 180° W longitude is west. Everything from from 0° longitude to 180° E longitude is east.
Any other "East/West" notation would be strictly political and can change overnight.
http://wwp.greenwichmeridian.com/