Nosecones are swapped between the fleet frequently from an engineering perspective, it’s easy. From a branding perspective, it looks rubbish. A good % of the A320 fleet were painted a different shade of white and/or have the blue at a different level. The B744/B777 fleet also have the mismatched shades of white. That could be fixed by sourcing the right colour from a retiring aircraft but that involves man hours and “cost cutting is now in BA’s DNA” as someone ex Accenture once said.
The worst example is the BOAC B744 retrojet which now has a spanking off-white nose. It looks terrible!