Such colourful designs are just a tissue of lies (4,4)
I believe the answer is:
fair isle
'such colourful designs are' is the definition.
The definition suggests a singular noun which matches the answer.
'just a tissue of lies' is the wordplay.
'just' becomes 'fair' (just can mean fair in the sense of showing justice).
'a tissue of' indicates anagramming the letters (a tissue can mean a tangle or mess of material).
'lies' is an anagram of 'isle'.
'fair'+'isle'='FAIR ISLE'
Can you help me to learn more?
(Other definitions for fair isle that I've seen before include "Jumper" , "Traditional knitwear design" , "Fabric pattern" , "British shipping forecast area - style of knitwear" , "Type of knitwear design" .)