Click on the picture that you'd like to colour, and a window should open** with the PDF picture in it.
Click on the print button in the toolbar or choose FILE>PRINT from the menu.
Choose the number of copies, etc. and then click OK.
** If you do not get a window, it means that you do not have the Acrobat plugin for your browser and instead you will get a file download box. Download the file to disk and open it from there - then proceed to step 2.