Birds appearances change through the seasons, but they don't all have the same methods for getting into their spring plumages ready for their nuptials.
The Starlings we see now are still in their winter plumage, with lots of spots and buff edges to their feathers, but in the summer they become pretty much black all over. The change comes because tips of the feathers they acquire in the autumn slowly wear off to leave them with their black suits. Personally think the winter outfit is more fun. They males and females are almost identical to look at, but in summer the colour round the base of the bill is bluish in the male and pinkish in the female, quite traditional really.
The Chaffinch is another that wears away the tips of the feathers to get into its breeding plumage, but unlike the Starling they are very dowdy in the winter and much smarter in spring.
Although wear does brighten up the Goldfinch, the red round the face getting redder and white underparts getting whiter, the basic pattern of the Goldfinch doesn't change much and by now they are looking pretty bright.
Black-headed Gulls loose their chocolate brown heads in winter (they aren't really black at all) and most have still got pale heads with various amounts of dark blotches on them. To get their "black" heads in summer they actually have a partial moult, growing new feathers for the season. This bird was in the Bay today and was the first I've seen this year already in summer plumage, some don't get theirs until April, so this is really an early bird.