When I print from Illustrator 3 to a Xerox printer, my bright yellow prints bright yellow. When my project is sent to a HP Designjet T1100ps plotter/printer, my bright yellow prints as an orange color. How do I fix this? What am I doing wrong?

Elizabeth,

Are you sure that the latter does not perform some colour management?

Also, is the Xerox CMYK and the Designjet RGB? If so, then the Designjet is converting the colors in order to print. Check which mode is required and make the file in that mode to begin with.

I was wondering if you could ever get them to look the same. It's two
different printers on two different papers. Still, you'd think they could
be closer than you're getting.
Richard