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)
Test Status | Color | Description |
|---|
Passed Test | Dark Gray | Initial hardware configuration tests passed |
| Light Gray | Initial system software tests passed |
| White | Final initialization test passed |
Failed Test | Red | ROM error |
| Green | Chip RAM error |
| Blue | Custom chips error |
| Yellow | 680x0 detected error before software trapped it (GURU) |
Here's something you might want to try to help fix your Amiga.
http://qa.retro-commodore.eu/index.php?qa=9&qa_1=what-can-i-do-to-fix-my-amiga-im-no-technician