It uses the border color to signal error codes if the main screen memory is corrupted.
Testing the internal beeper or the AY-3-8912 sound chip. Top ZX Spectrum Diagnostic Test Programs zx spectrum test program link
| Border Color | Meaning | |--------------|---------| | | CPU test passed, beginning RAM test | | Red | Fatal error: CPU or ROM addressing fault | | Green | DRAM test in progress | | Cyan | Lower 16K RAM (bank 0) passed | | Yellow | Upper 32K RAM (banks 1-3) testing | | Magenta | RAM refresh failure (timing) | | Black | All tests passed – but with rapid flashing? Wait, no – steady black indicates halted CPU. | It uses the border color to signal error