Fruits are typically harvested before they become ripe to allow time for transport.
A ripe fruit will give somewhat if squeezed, similar to an avocado. Too much give means the fruit is likely to be overripe.
For typical dragon fruit varieties, this means bright, vibrant fuchsia to red coloring and scales tipped in lime green to yellow.
Some discoloration is expected on ripe fruits and is often indicative of flesh that has begun to sweeten.
Ripe dragon fruits can be stored on the counter if you plan to eat them within a couple of days.