Maybe it got lost in translation? I get that a lot with Chinese manhwas too, where an exact translation doesn't make sense but it does in the og language bc of Chinese characters etc... So maybe it does hold an importance in the native language but it doesn't make sense in English
It sounds like they are just very on the nose names- Kanna said that the carrier pigeons worked so hard that they didn't get a chance to be washed. So presumably they turned black. Blue stain probably has something to do with a stain that is blue.
I think whoever named them in the story may need to be given a new job though, they obviously have no imagination and shouldn't be naming things!
Tbh, if I was translating and saw those two shitty ass names, I’d be doubting my eyes. Cause the author really flipped at random through an English dictionary for four words, and smashed them together.