Large flag inside hotel the colour of mud (11)
I believe the answer is:
hearthstone
'large flag' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
'inside hotel the colour of mud' is the wordplay.
'inside' means one lot of letters goes inside another.
'hotel' becomes 'h' (phonetic alphabet: alpha, bravo, charlie etc.).
'the colour of' becomes 'stone' (I can't explain this - if you can you should give a lot more credence to this answer).
'mud' becomes 'earth' (I've seen this before).
'h'+'stone'='hstone'
'hstone' enclosing 'earth' is 'HEARTHSTONE'.
Can you help me to learn more?
(Other definitions for hearthstone that I've seen before include "Material forming a fireplace" , "One may be under fire" .)