The maps are large so don't copy if you have a query pls. Hopefully, they provide geographic clarity.
This is the current network to give you an idea of change;
http://www.bts.co.th/customer/en/02-route-current.aspx
The urban rail site gives a clear sense of what lines are currently being constructed as per (B) in the above list (though the SRT Dark Red line is not included as it is technically a suburban line);
This is the current Master Plan which has been refined and changed over the last decade - though you won't see some of the above listing on this map as they have been proposed more recently, eg. The Brown Line.
Some lines may be easier to understand in this version which includes all proposed lines and those under evaluation. Completed by Skyscraper City member Archstudent;
Thai language version -
http://upic.me/i/cs/bangkok_mrt_masterplan_3.jpg