Any peach variety is delicious in this coffee cake, from fruits that are bright yellow-orange with a rosy blush to those that are the palest white. Even ripe peaches, however, may be difficult to peel. To peel them easily, bring a saucepan three-fourths full of water to a boil. Using a small, sharp knife, cut a shallow X on the blossom end of each peach. Immerse the peaches in the boiling water for 20 to 30 seconds. Lift out with a slotted spoon and let cool on a work surface. Using your fingers or the knife, slip off the skins.