Your code for changing the screen colors works well, but it doesn't change the crosshair colors. This results in crosshairs the same color as the background :-)

This is what I ended up with:
Thanks for the huge jump-start!!!
Mike Weaver

;CODING STARTS HERE
(vl-load-com)

;Toggle Paper Space
(defun c:pswhite()(screencolors nil 16777215 0)(princ))
(defun c:psblack()(screencolors nil 0 16777215)(princ))
(defun c:psgray()(screencolors nil 5592405 5592575)(princ))

;Toggle Model Space
(defun c:mswhite()(screencolors T 16777215 0))
(defun c:msblack()(screencolors T 0 16777215))
(defun c:msgray()(screencolors T 5592405 5592575))

;;; mspace nil - use paper space
;;; mspace T - use model space

(defun screencolors(mspace bkgrnd crshrs)
(setq acaddisplay (vla-get-display (vla-get-preferences (vlax-get-Acad-Object))))
(if (null mspace)
(progn
(vla-put-GraphicsWinLayoutBackgrndColor acaddisplay bkgrnd)
(vla-put-LayoutCrosshairColor acaddisplay crshrs)
);progn
(progn
(vla-put-GraphicsWinModelBackgrndColor acaddisplay bkgrnd)
(vla-put-ModelCrosshairColor acaddisplay crshrs)
);progn
);if
(princ)
);defun
(princ)
;CODING ENDS HERE