Partly coloured feathers are very unusual in leucism. Individual feathers that are partly coloured usually indicate a bad condition of the bird during feather growth and is not an inherit- able character (ie, is not leucism). This is often seen in, eg, Carrion Crows, especially those eating junk food in cities.
Blackbirds with white feathers on their heads or bodies are leucistic. You can see one in this post. Leucism is an inherited trait distinct from albinism, when animals are unable to produce melanin (a black pigment) at all on their bodies, resulting on all white individuals with red eyes. This doesn't affect carotenoid (yellow, red, orange) pigments, so these colours are unaffected if the normal bird displays them, e.g. an albino blackbird will have a yellow/orange bill (see an example here).
van Grouw, H. (2006) Not every white bird is an albino: sense and nonsense about colour aberrations in birds. Dutch Birding, 28(2), 79-89. here.