Try 1st change to Autocad PDF High quality print maybe. There may be a dpi setting increase somewhere also.
Have found like you some colors change maybe they can be set to rgb you can edit the ctb saves as a copy Mypdf.ctb. lee-mac has color lisp so you put in number a rgb will come back
;; ACI -> RGB - Lee Mac
;; Args: c - [int] ACI (AutoCAD Colour Index) Colour (1<=c<=255)
(defun LM:ACI->RGB ( c / o r )
(if (setq o (vla-getinterfaceobject (LM:acapp) (strcat "autocad.accmcolor." (substr (getvar 'acadver) 1 2))))
(progn
(setq r
(vl-catch-all-apply
'(lambda ( )
(vla-put-colorindex o c)
(list (vla-get-red o) (vla-get-green o) (vla-get-blue o))
)
)
)
(vlax-release-object o)
(if (vl-catch-all-error-p r)
(prompt (strcat "\nError: " (vl-catch-all-error-message r)))
r
)
)
)
)
(LM:ACI->RGB 10) 255 0 0
(LM:ACI->RGB 30) 255 127 0