Can bird's feathers be dyed? I know that bird's feathers (and beak) can be dyed on a temporary basis e.g. when eating food that is highly coloured such as berries or beetroot or carrot. They can also get temporarily stained if they brush against toys that have been dyed with water-soluble vegetable dyes. But this dye fades when the bird has a bath or cleans its feathers. And the vegetable dyes are non-toxic or have health benefits (e.g. eating carotenes) so ingestion during play or preening is not a risk.
Could the feathers be dyed with a 'permanent dye'? No, they could not. I believe that any attempt to do so would cause serious harm to the bird (1) because permanent dyes are toxic and would be ingested and poison the bird. (2) because the dye would affect the properties of the feathers so that downy feathers could not remain fluffy and so maintain the bird's body temperature correctly and flight feathers would not be efficient for flying (3) because the dyeing process would terrify the birds. These stresses would be magnified for baby birds and probably kill them.
In addition to the animal welfare issues, there are consumer protection laws to consider too. I believe that to dye a bird in order to give a false impression would be a form of fraud, for which a seller might expect criminal prosecution as well as civil action (being sued).
Here in the UK, dyeing a bird would probably result in criminal prosecution under animal rights and animal welfare legislation. You could expect fines and/or a prison sentence. You would also face prison for fraud and if you conspired with others in a scheme to cheat buyers by selling dyed birds you might be prosecuted under legislation dealing with criminal conspiracy and organised crime. There would be a heavy prison sentence for this too. Given the popular hatred towards those convicted of animal abuse, you would probably not enjoy your time inside once other inmates knew what you had done.
I think any decent person would not even consider dyeing birds. But if there are irresponsible people reading this, who do not give a damn about animal welfare and think dyeing birds might be a clever way to make easy money, then maybe they will have second thoughts when they consider the prosecutions they would be liable to.
Personally, if I suspected anyone was attempting to dye birds, I would not hesitate to report them to the police and the RSPCA. I am so offended by the very idea of doing this that I am struggling to keep this reply civil. I hope I have succeeded but if not then I hope the reader will understand my outrage.