bootloader – Where is Boot flow screen displayed in android

I have came across Boot flow and when there is based on boot state of a device, it shows different colot screen.

YELLOW: Warning screen for LOCKED devices with custom root of trust set
ORANGE: Warning screen for UNLOCKED devices
RED (eio): Warning screen for dm-verity corruption
RED (no os found): No valid OS found

Let me know where or from which path those screens are displaying?

Eg:Yellow Screen