More to do with the way the data is being sent from the computer.
Try a few tricks to see what happens.
For example , I asume you are printing dirvctely from nhe downloaded page.
Try saving them to a folder and then later print from the saved file.
Also you say you use only black, if this is a normal 4 colour printer then you are printing all colours.
Black is made up of all colours.
If you are using a 'black only' facility[some printer have this]
Then all the text that is coloured and the colour photos will reproduce un vaying shades of grey.