What colour is consciousness? How high is it, how wide? And would it look better with stripes or stars?

No they're not silly questions, they're trying to illustrate that the mind simply can't grasp consciousness itself because consciousness is so far beyond the mind. In mediumship there's a saying - "All Spirits are thirty-five years old." Of course Spirit doesn't have an age but by looking thirty-five years old Spirit conveys the consciousness that they are in the 'prime of their existence' just like being thirty-five is being in the prime of our Lives.

You expectations don't give them Life, your expectations help create how you perceive them. Call it a mental picture if you like, in the way you create a mental picture of people you regularly interact with in these forums. Spirit Guides are not archetypes though, while the conscious mind perceives them in much the same way archetypes are internal (either personal or collective) and Spirit Guides are external. However, both are 'representations' of consciousness.