Colour an Irishman goes about in (5)
I believe the answer is:
paint
'colour' is the definition.
(I know that paint is a type of colour)
'an irishman goes about in' is the wordplay.
'an irishman' becomes 'Pat' (Patrick is a common Irish name).
'goes about' means one lot of letters goes inside another.
'pat' going around 'in' is 'PAINT'.
(Other definitions for paint that I've seen before include "Catch a likeness" , "Coloured liquid in tins" , "Eg, emulsion or gloss" , "Apply a coat of colour" , "Decorative coating" .)