Fascia sombrely reflected tile design (6)
I believe the answer is:
mosaic
'tile design' is the definition.
(I've seen this in another clue)
'fascia sombrely reflected' is the wordplay.
'MOSAIC' is hidden backwards in amongst the letters.
However, I'm unsure how the hidden word is indicated.
Can you help me to learn more?
(Other definitions for mosaic that I've seen before include "Picture/pattern in small coloured pieces" , "Tessellated pattern" , "piece of artwork" , "Picture made up of coloured fragments" , "Inlaid work - of a Hebrew prophet" .)