Radomes (nose?) are interchangable. Example, you can take one off any 737 and put it on any other 737 without modification to the radome or airframe. By painting the radome a single color like black or white you don't have to worry about any logos/paint schemes lining up, from aircraft to aircraft.
Or the old radome was damaged and the new one won't get painted until the next repaint, happened a lot in my day
A bit of thread drift, but it wasn't only radomes. I recall seeing at least one BAC 1-11 with a rudder painted in one BA colour scheme and the rest of the aircraft painted in another. I forget whether the rudder or the rest was the more up to date.