The half-buried fallen fruit of a Coconut Palm (Cocos nucifera) gamely sprouts in rocky alkaline soil along the beachfront at Kealia Beach, Kapa'a, east Kaua'i.
This VERY mature coconut (Cocos nucifera) has just begun to dry out in the sun; its exocarp has lost its color and the fibrous coir of the mesocarp is beginning to show through.
Here is a photo of an immature coconut (Cocos nucifera) that has just been opened to show the innards. The outer layer (exocarp) is greenish yellow (immature) to light yellowish brown (mature). The husk (mesocarp) is brown colored and composed of numerous thick fibers (coir). The inner "stone" (endocarp) is extremely hard, woody and hairy; it is the part of the fruit sold in US mainland stores as a "coconut." In the image the "meat" and "milk" has been removed.
This coconut (Cocos nucifera) has been drying in the sun for a long time and the fibrous husk (coir)  of the mesocarp is now plainly visible. Soon the hard inner core of the nut will be visible.
This and the following sequence of photographs shows the stages of development of the fruit or DRUPE (the coconut fruit is not a true "nut") of a Coconut Palm (Cocos nucifera). 

This image shows immature coconuts (fruits) that are still green.
These coconuts are well along in the ripening process, just beginning to turn brown and developing a thick outer husk (or exocarp). If left unharvested, the nuts will harden and dry out, eventually dropping to the ground when completely ripe. 

One of the hazards of living with coconut palms is that the large, heavy nuts commonly dislodge from their stems when ripe and fall to the ground with a good deal of force. I've never been konked by one of these but have come close on several occasions.
The half-buried fallen fruit of a Coconut Palm (Cocos nucifera) gamely sprouts in rocky alkaline soil along the beachfront at Kealia Beach, Kapa'a, east Kaua'i.
The half-buried fallen fruit of a Coconut Palm (Cocos nucifera) gamely sprouts in rocky alkaline soil along the beachfront at Kealia Beach, Kapa'a, east Kaua'i.
The half-buried fallen fruit of a Coconut Palm (Cocos nucifera) gamely sprouts in rocky alkaline soil along the beachfront at Kealia Beach, Kapa'a, east Kaua'i.
See photo in original gallery.