OK the next puzzle is also pretty straightforward. You've got these lightposts all over creation and obviously have to do something with them :) Follow them to the beach by the yellow one - you'll find a big red one. Spin this four times in order to start light shining down them. You'll see pretty obviously when the light goes from one to the other.

OK, back to the yellow one. Look in it until you see the blue one. Now on to the blue, point it at the green one. Point the green one at the red one, red one at the yellow one, yellow one at the purple one, purple at the red one, and then the red one at the focusser at the leaf door. You now have to get over there and press those same colors in order:
yellow, blue, green, red, yellow, purple, red
It'll open up.

Once again, you can't actually get the book until you go and chat with Saavedro inside the middle.

This book leads to Voltaic. The code is 7:00, 9:00, 5:45, 4:00.

The Myst 3: Exile Walkthrough