For peaches and nectarines, aroma and degree of softness are more telling than color, although a peach that's hard and green near the stem is probably not ripe. Be gentle when checking softness. Use your finger pads rather than your finger tips, which are more likely
Hard: The peach feels like a baseball and should not have been picked.
Firm: It feels like a tennis ball and may be ready to enjoy in a few days.
Give: A peach with a little give -- it absorbs subtle pressure, but does not bruise -- is the most versatile fruit. It's on the edge of its most powerful flavor and can ripen a bit more or be used for baking.
Soft: Ready to be eaten fresh. The fruit will bruise easily, so handle with care. Soft fruit can also be used for cooking and baking.
Gushy: Heavy with juice, this fruit is enjoyably overripe. It may be a bit bruised, but it's perfect for jams or purees. You probably won't see this stage at the market, but you might at U-pick farms and on backyard trees.
Bruised: Don't worry about flattened and indented areas with slightly discolored flesh. The bruising can be cut away, and it indicates a ripe piece of fruit.
Mealy: This frustrating state indicates cell structure breakdown caused by cold storage. The texture can be soft, but such fruit will never ripen correctly.
P.S. Ripen fruit by resting it on its shoulder so it does not touch other fruit. Refrigerate ripe fruit to stop the maturing process, if it can't be eaten immediately. You'll get the best flavor hit if you bite first into the sun-kissed end opposite the stem.