When dragon fruit is becoming ripe it becomes red or yellow depending on the type of dragon fruit.
Once dragon fruit has become fully ripe the dragon fruit skin should become bright and even colored which means it's ripe and ready to eat.
Blotches or what looks like bruises on the skin of dragon fruit can mean that the dragon fruit is overripe.
But some spots on the dragon fruit skin are normal and even over ripe dragon fruit can be eaten however it may not taste as good.