The brightly coloured danios - the neon coloured ones - are glo fish. These are genetically modified with jellyfish genes, and GM organisms are banned in the EU - we may have left but the law still stands. There are other species of glo fish now including white widow/skirt tetras and bettas. They are also illegal.
The tattooed and dyed fish tend to be pale coloured fish, and it is illegal to tattoo or dye them in the UK but not illegal to import fish tattooed/dyed elsewhere which is why you sometimes see them in shops.
The tattooed and dyed fish tend to be pale coloured fish, and it is illegal to tattoo or dye them in the UK but not illegal to import fish tattooed/dyed elsewhere which is why you sometimes see them in shops.