We colorized our CTB this past year and we had a similar graying issue when piloting from AutoCAD or PDF with the new CTB. It relates to how each program handles colors, short of Adobe and Autodesk locking some programmer is a room together to figure it out, it's probably not changing. Our work around was to assign a darker shade to the plot color for a given screen color we liked, i.e. Screen color 130, plot color 138. It let us produce color PDFs that were still readable when printed on a B&W laser printer. Yes, the color is darker on the PDF or color print than the screen, however if you're using a black background in your work space having a brighter screen color pops a bit more. YMMV depending on what you're attempting to visually accomplish.