This seems to be the most commonly planted shrub in all of Honolulu, and it does look sort of familiar, but not familiar enough. The first two photos are from the road leading to Lyon Arboretum; these plants had no flowers. The other photos are from Foster Botanical Garden (obviously way too common to merit a sign), but really, it's planted all over the city. Nobody I asked knew what it was though. Leaves seem to be opposite, around 10-13cm long. Flowers are maybe 2cm in diameter.
It looks like Pseuderanthemum carruthersii var. carruthersii 'Reticulatum'. Common name Yellow-Vein Eranthemum, Golden Pseuderanthemum http://hortpics.org/gallery/view/aca/psecacare/ https://toptropicals.com/cgi-bin/garden_catalog/cat.cgi?uid=Pseuderanthemum_reticulatum&comments=1