We have two presses and you must select which press you want it to go to at the time of uploading.  If you upload a b/w file and you select color interior it will go to the color press, if you upload a color file and you select b/w interior it will go to the b/w press.  Replacing the interior file does not change the press the file is sent to.  This is important as the color press is substantially more expensive because of the type of ink and paper used.  If you selected the wrong press you will have to upload the files and select the correct press from the beginning.