The neighbour of Violet Jones, the architect, collects diamonds (6)
I believe the answer is:
indigo
'the neighbour of violet' is the definition.
'indigo' can be an answer for 'violet' (indigo is a kind of violet). I'm unsure of the 'the neighbour of' bit.
'jones the architect collects diamonds' is the wordplay.
'jones the architect' becomes 'Inigo' (Inigo Jones, 1573-1652).
'collects' means one lot of letters goes inside another.
'diamonds' becomes 'd' (abbreviation in bridge say).
'inigo' going around 'd' is 'INDIGO'.
Can you help me to learn more?
(Other definitions for indigo that I've seen before include "Spectral colour" , "Blue/violet dye" , "Violet dye" , "Natural blue dye" , "product of woad" .)