It's not Japan in the autumn but Samoa does have a fair splash of colour in its local flora. The one flower I must mention is Samoa's national flower, the teuila. It's a beautiful brilliant red/pink and is visible throughout the country. I'm pretty sure it's found throughout many Pacific nations but only Samoa lays claim to it as a national flower. And only Samoa has a week-long festival named after it.
I've been taking photos of flowers and other flora on and off over the months as I've made my way around the country. Here a few I've taken. Enjoy.