The BIOS expects a 8-bit (256-color) palette, but you provided 24-bit. Fix: Convert to 8-bit indexed BMP. Ensure the palette has black (#000000) at index 0.
Using tools like UEFITool , PhoenixTool , or InsydeFlash , modders extract the LOGO module from a stock BIOS, replace the embedded bitmap, and then "patch" the module’s checksum. This creates a —one that is functionally identical to the original except for the logo.
This is the most critical part of the query. You cannot simply rename a JPEG to .bmp and upload it to the BIOS.