There are two main classes of melon, the muskmelons and the watermelons, and each class has a wide range of different varieties in the class.
Watermelons can be grown in all sorts of shapes and sizes (including the new square ones from Japan) and come in a variety of colors. The flesh can range from white to a deep red, with newer varieties being prized for their deep gold and bright orange colors. Some watermelon varieties have seeds in a wide range of colors, including even green or reddish seeds. Seeds are optional now as many watermelons are available with small soft wide seeds rather than the traditional hard black ones we are used to. The so-called "seedless" watermelon varieties fall into this category and you can either eat or discard the small pale seeds. Watermelon seeds are actually prized in some cultures and are cooked and included in a wide variety of dishes. The rind is also used in a wide variety of sweet and savory dishes, even in the United States. The most popular usage of the rind is probably in watermelon pickles, which were very popular around the turn of the century. Watermelons are in peak season in the United States from mid-June to late August.
The second group of melons are muskmelons, and they basically include every type of melon that is not a watermelon. The most common muskmelons are cantaloupes, honeydews, casaba, cranshaw, Juan canary, and Santa Claus melons. Muskmelons are further broken down into two groups, those with smooth skins like the honeydew and those with a netted skin like the cantaloupe. They range in size from slightly larger than a softball to really large 15 pound varieties. They come in a wide range of colors, both on the outside and the inside. The skin can range from a pale grayish white to very dark green and the flesh ranges from the palest of yellows to the brightest of oranges and greens. All muskmelons have hollow seed filled centers rather than seeds dispersed throughout the flesh. Most varieties of muskmelons come into season during the late summer and early-mid fall.