Novel trade company's colourful style (3,4)
I believe the answer is:
art deco
'colourful style' is the definition.
'art deco' can be an answer for 'style' (decorative style). I'm not sure about the 'colourful' bit.
'novel trade company's' is the wordplay.
'novel' is an anagram indicator (letters in a new or novel order).
'company' becomes 'co' (abbreviation).
'trade' anagrammed gives 'artde'.
'artde'+'co'='ART DECO'
Can you help me to learn more?
(Other definitions for art deco that I've seen before include "1920s and 30s style of art and architecture" , "style of interior design" , "Architecture and design movement of the 1930s" , "modern style" , "Old style" .)