Well, you never know.
I would never advocate doing this deliberately, but here's what happened when we bought our pair from a bin-o-budgies store, expecting that the staff would know what they were doing.
We picked one blue and one classic green, both lively. They lived in separate cages at the store, not in view of each other. The clerk swiped them up and put them into a single box for us to carry home. And we popped them straight into our one cage when we got home. The poor things sat in opposite corners for a few days...
I guess the good part is that neither one felt it had the right to be territorial. It took them a few weeks to really make friends, but they didn't seriously fight.