How to create semi-transparent image using imagemagick

Question

I have a hex (i.e. #FF0000) color and want to generate 50% transparent 50x50 image using imagemagick from command line.

Answer 1

I had to figure out something similar when I was working with CSS 3 and RGBA.

convert -size 50x50  xc:'rgba(255,0,0,0.5)' red_0.5_pixel.png