Colour of originally popular cat breed (8,4)
I believe the answer is:
prussian blue
'colour' is the definition.
(Prussian blue is an example)
'originally popular cat breed' is the wordplay.
I cannot really understand how this works, but
'cat' could be 'russianblue' (I've seen this before) and 'russianblue' is found within the answer.
A single letter 'p' remains which might be clued in a way I don't understand.
This explanation may well be incorrect...
'of' acts as a link.
Can you help me to learn more?
(Other definitions for prussian blue that I've seen before include "Deep-coloured pigment" , "Pigment used in painting and dyeing" .)