Splashing of paint that's not suitable (5)
I believe the answer is:
inapt
'not suitable' is the definition.
(I've seen this before)
'splashing of paint' is the wordplay.
'splashing of' indicates anagramming the letters (I've seen this in other clues).
'paint' with letters rearranged gives 'INAPT'.
'that's' is the link.
(Other definitions for inapt that I've seen before include "Unsuited" , "Cartoon duck" , "Ill-suited" , "Not suitable or appropriate" , "Not fit, unsuitable" .)