01/07/2014 AT 04:05 PM EST
On Sunday, Reese Witherspoon
bared her bikini body, looking pretty in purple while visiting Oahu, Hawaii.
The mom of three coordinated her bright bikini with gold hoop earrings, beige shades and layered, beaded necklaces. Her 4-carat custom engagement ring
from husband Jim Toth
added extra sparkle to her beach ensemble.
Witherspoon, 37, was on the island to attend actor Justin Bartha's wedding
to fitness trainer Lia Smith, but managed to find time for some fun in the sun, posting photos of the ocean, sand and her beach read
, David Sedaris's, Let's Explore Diabetes with Owls
The key to her toned and taut figure? Exercise, even when on vacation.
"Gorgeous day for a run on #WaikikiBeach," she Tweeted