If you are using Chrome to print invoices, then you need to enable Background Images on your print dialog for the blue bar over the invoice's items to print.
STEP 1: Click More Settings at the bottom left of the Print dialogue.
STEP 2: Notice the empty checkbox next to Background Graphics, and notice that in your print preview, the blue bar does not print. Check the Background Graphics checkbox.
STEP 3: Now you see that the blue bar displays in the print preview, so when you print your document, the blue title bar will print.