A cantaloupe is ready to harvest when there is a crack in the stem and when the rind changes from green to yellow or tan. Don't use the color on its own to determine if the fruit is ripe, but look for the crack and other signs as well.
A good rule of thumb is that if the cantaloupe is easy to pull off the vine, it is ripe enough to be harvested. However, if it falls off on its own, it might already be overripe. Do not harvest the cantaloupe until the vines are dry, or they might get damaged when pulling the melon from the vine. The melon doesn't get any sweeter once it is off the vine, but it does begin to soften. Store it uncut for up to six days or cut in the refrigerator for up to three days.