Your answers are right on the money
It bothered me when we had so many all-white aircraft, particularly amongst the Boeing 737 fleet. Now JAT is down to the last two 737s that require a fresh coat of paint. The next in-line to receive new paint will be the YU
-ANH, likely followed by the YU
As for the DC-9s, those planes will be exiting the fleet later this year, so there is no point in wasting money on a new paint job now. BTW, the two DC-9s are in fact fairly busy. They fly primarily from Belgrade to Brussels, Milan, Rome, Athens, Istanbul and odd flights to Zurich, Frankfurt, Podgorica, Tivat, and Ljubljana.