How can I print in colour from mac book air when olivetti printer defaults is set to print mono
For this answer, I am assuming that you are using a relatively newer version of OS X on your Mac and at least Windows 7 for the HP Pros.

This is a driver issue.  The only thing that can override a default value is a user setting on a driver.  I went to the Olivetti MF 2400 support site and found these drivers:



If you notice, there are two MacOSX drivers that are "PS Mono;"  that's Post Script Monochrome.  I suspect you are using one of those drivers.  Try downloading and using the "PS" version of the driver (the second one being that it is for 10.6 which is the version of OS X that only supported the Intel CPU and not the PowerPC.

That said, this is a discontinued printer and finding drivers may become much more difficult as time progresses.  You may be able to extend its useful life by sharing this printer (via CUPS in Linux/Unix) and emulating something a bit more generic like an HP Color Jet.  It's not the cleanest solution, but if you just want basic color printing, it will probably get the job done.