The bootup screen colors mean something for each color. If you don't end up seeing the bootscreen, you might see these colors.
For black screen the system doesn't work and doesn't even start the initial selftest.
Quoting the Amiga 4000 User's Guide (Chapter 7-3) below (ED: The Passed test colours have been modified to fit the actual screen, it says Light Gray for all 3 in the manual, but the screen changes colors)
Initial hardware configuration tests passed
Initial system software tests passed
Final initialization test passed
Chip RAM error
Custom chips error
680x0 detected error before software trapped it (GURU)
Here's something you might want to try to help fix your Amiga.