Paint, true, when splashed around, gives measure of warmth (11)
I believe the answer is:
temperature
'measure of warmth' is the definition.
(I've seen this before)
'paint true when splashed around' is the wordplay.
'paint' becomes 'tempera' (tempera is a kind of paint).
'when splashed around' indicates anagramming the letters.
'true' with letters rearranged gives 'ture'.
'tempera'+'ture'='TEMPERATURE'
'gives' acts as a link.
(Other definitions for temperature that I've seen before include "Degree of hotness" , "Measure of warmth" , "Measure of heat" , "Degree of heat" .)