A high-quality tea Mark’s passed up in Coloradan town (7)

'coloradan town' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.

'a high-quality tea mark's passed up in' is the wordplay.
'a' becomes 'an'.
'high quality tea mark's' becomes 'assam' (I am not sure about this - if you are sure you should believe this answer much more).
'passed up' says the letters should be written backwards.
'in' is an insertion indicator.
'assam' backwards is 'massa'.
'an' put into 'massa' is 'MANASSA'.

Can you help me to learn more?