As usual, I am stuck on the last two, which seem to be differnet from the clues that stumped everyone else!
7a Colour telephone holding one back (5) -I-A- My feeling is that the answer is TITAN (Ttian without 1 i), but I cannot see where the telephone comes into it!
and 15a Warm condensation on the radio (7) -U-M-R- I think this one may be SUMMERY, but again have no idea why!