Like cloverjo I have 'I' as the last letter of 20d. If 36a is TATS then the crossing cell must contain both the 'I' and the 'T'. Therefore one of the other two cells must contain two letters but both 5d and 26d are clues to entries that do not contribute to any coloured cells (I.e. cells containing two letters) as both 5d and 26d contain items to be removed before solving.
Have I misunderstood the instructions? (more than likely!)
Any help gratefully received!