1. A method of filling an image portion of a page to be printed with a corresponding color, said method being performed in a printer, said method comprising: receiving a plurality of commands specifying content for said image portion of said page, said image portion containing a plurality of points, said plurality of commands including at least one command specifying a raster operation to be performed to generate a bit map representing said image portion, said raster operation being performed on at least one operand, and indicating that said one operand is to be filled with corresponding color; determining for each raster operation whether performing said raster operation of said at least one command would result in a same value of said corresponding color being generated for all of said plurality of points of said image portion of said page; if said same value would be generated for all of said plurality of points of said image portion of said page, performing said raster operation for only one of said plurality points to determine said same value and using said same value for all of said plurality of points of said image portion of said page; and if said same value would not be generated for all of said plurality of points of said image portion of said page, performing said raster operation for each of said plurality points to determine a value for each corresponding point and using said value for said corresponding point of said image portion of said page.