I am finding that the latest TeXShop produces a greyed out PDF file after processing a source file that has a fatal error in it a very small number of times. Restarting TeXShop seems to fix the problem.
Note: there is no error message so far as I can determine. Further, the PDF file appears as it should when printed or if one goes to full screen display, say.
I am running TeXShop 4.27 and ConTeXt 2019.04.16 with macOS 10.14.4.