Highlighter colors look muddy when printed from Acrobat 8, X, and Reader XI to Xerox WC7775, 7665

Highlighter colors look muddy when printed to Xerox WC7775, 7665(applies to Acrobat 8 Std, Acrobat X Std, Reader XI).  I tried the latest PS and PCL6 drivers from xerox.com.  How can I troubleshoot / fix this so highlighter colors look bright when printed? 

When printing highlighted text from other applications (like Word) from the same computers to the same printers, the highlighter color is bright.  Users print PDFs for distribution to clients so they would like the printed documents to look good.

Thanks