The one doing somersaults, in blue (6)
I believe the answer is:
indigo
'blue' is the definition.
(I've seen this before)
'the one doing somersaults' is the wordplay.
I cannot really understand how this works, but
'one' could be 'i' (Roman numeral) and 'i' is found in the answer.
an anagram of 'doing' is 'ndigo' which is present in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
'in' acts as a link.
Can you help me to learn more?
(Other definitions for indigo that I've seen before include "Sixth rainbow colour" , "Blue-purple colour in spectrum" , "I of ROYGBIV" , "Deep violet-blue colour" , "Blue dyestuff" .)