The image aliases are created on demand, and are reused until the image cache is cleared. Something that only happens if you change the image to another one or specifically clears 'Cache for imagealias' on setup page.
"Reference" is the example in image.ini, the idea is that you have several aliases that for instance use grey colour. So "Reference" could be grey and the aliases that also needs to be grey inherit "Reference" as it's original image.