It it could also very well be that it is just unusual and not associated with danger, so it could be relaxing by lack of associations. In general anything more

It it could also very well be that it is just unusual and not associated with danger, so it could be relaxing by lack of associations. In general anything more complex than "birds like blue feathers because it shows a strong immune system" is unlikely to have a simple satisfying evolutionary reason to exist that is less than 80% wrong.