What is UEFI based on motherboard manufacturers?

Question

Iron

From manufacturers such as Asus, MSI, Asrock, etc. UEFI looks almost the same, only they change the color theme and the arrangement of elements, which means that they probably use the same operating time. So what do they use as a basis?

Answer 1

Usually there is a customized AMI BIOS. At least on Intel I only saw such.
You can download UEFITool and poke images.

Answer 2

Any UEFI based on Linux