Why can't I print the colored part of an article in Wikepedia?

It could be that Wikipedia has "print" CSS which renders it differently to printers, or you may have no colour ink left in your printer, or the printer driver may be set up to print in black and white. You can test these things by trying printing something else in colour (proves there is still colour in your printer). Also take a screenshot of the Wikipedia page and print that (if it prints in colour then it was a CSS issue).

yes thats right. you should check the printer first. may be it lack the colored ink.