It's obviously true the Saltire is there, present within the Union flag, but the Saltire also exists outside the Union flag, and as I said, Scotland never had any Empire of any significance when the Saltire alone was in use to represent Scottish nationhood, whereas the Empire itself only existed as a notion after the advent of the Ensign of GB and then the Union flag.
It's hardly a stretch then, to point to this as the obvious reason why the Union flag might be perceived to have connotations of Empire that the Saltire does not.
I am not, and never was, attempting to make any point whatsoever about Scots participation in the Empire, aside from admitting their active part in it, merely to point out why one flag might carry connotations that another does not, which was the original question, not whether or not Scotland played a part in Empire and/or Scots in Imperialism.
If some people perceive the Saltire to be representative of a Colonial past, then I would not argue with that perception because Scotland is undoubtedly a major participant in the UK and GB's colonialism, however, I've never heard the Saltire described as a symbol of Imperialism, or that claim made about it, whereas I've heard that claim made for the Union flag repeatedly.