Anyone have any idea why the following metapost included in a layout causes the error below?

It is almost identical to code extracted from data.mp, yet it upsets therion (I have added the 237 so you can see where the error occurs).

       code metapost 

                        %define colours for custom water point & area background

237                   color colour_water;

                        colour_water :=(226/255,244/255,253/255); %light blue

                        color colour_sump;

                        colour_sump := (22/255,22/255,95/255);    %dark blue

       endcode

D:\Program Files\Therion\therion.exe: error -- ../../StdFiles/LayoutStandards.thc [237] -- ../../StdFiles/LayoutStandards.thc [237] -- not enough option arguments -- color -- must be 2

Regards

Bruce