Contrast. Yes. I think that could be the answer, even though I never had the situation where there was nothing. I believe Stuart Little's tutorial had a bit about that. Also perhaps here
http://ianlangelectronic.webeden.co.uk/#/lcd-module-0/4569058582
I believe the contrast requirement varies according to what is on the screen and, consequently, striving for good graphics contrast is not worth the effort. I believe I modified the Philips pcd8544 library with Lewis's contrast setting.