How to use Alpha channel in GOP Framebuffers?

While developing an operating system, I can draw a shape with any color with 0xFFFFFFFF, All RGB Channels are working but Alpha channel is not working why?

And How can I make Alpha channel work?

I am using GOP Framebuffers;

void PlotPixel(uint32_t x, uint32_t y, unsigned int color) { buffer->baseAddress + (x*4) + (y * buffer->PPSL * 4) = color; }

PlotPixel(400, 450, 0x6EFFFFFF);

https://wiki.osdev.org/GOP