What all characters appeared regularly in black and white shorts but had actually debuted in color cartoons?

Disney
Donald Duck appeared in The Wise Little Hen and then co-starred in a number of black and white Mickey Mouse cartoons.

Warner Bros.
Porky Pig debuted in I Haven't Got a Hat before regularly appearing in black and white Looney Tunes, rarely appearing in any other color Merrie Melodies until the Looney Tunes series switched to color.

Beans the Cat is the same case, debuting in I Haven't Got a Hat and then all of his later appearances were in black and white cartoons (the same can be said about most of the I Haven't Got a Hat cast, though I feel none of them besides Porky or Beans really starred in many cartoons).

Bugs Bunny debuted in A Wild Hare, and made cameos in a handful of black and white cartoons (Porky Pig's Feat and two Private Snafu shorts). Probably shouldn't count, since Bugs never starred in any black and white cartoons and his only appearances in black and white were as cameos.

Are there any other characters?

Flip the frog debuted in color in Fiddlesticks.

Some of the characters in Fleischer's "Guiliver's Travels" (1939) appeared in some black and white shorts.

Also, Terrytoon's Sourpuss, who debut in color, appeared in some black and white cartoons including his first meeting with his soon-to-be costar, Gandy Goose.