An arcade game released by Taito in 1987, and subtitled "The Story Of Bubble Bobble 2". As this suggests, it was the sequel to their popular previous release titled "Bubble Bobble".
The gameplay is vertical-scrolling platform style, and very similar to Bubble Bobble. Players use the characters Bub and Bob to proceed through seven levels filled with monsters, and with four stages to each level. Each level culminates in a battle against an end of level baddie. However unlike Bubble Bobble, the characters are in human form and employ rainbows to defeat monsters. Collecting power-ups increases your rainbow power, and food items similar to those in Bubble Bobble give you extra points. The feature in Bubble Bobble of collecting letters to form the word "EXTEND" and gain a large bonus is continued; however you now have to collect seven gems to make the colours of the rainbow.
Despite the insane popularity of Bubble Bobble, Rainbow Islands did not do so well. It had a similar style and equally addicitive gameplay to Bubble Bobble, but the characters in human form did not have the same mass appeal they did in bubble-blowing dragon form. Taito attempted to salvage the game in 1988 by releasing an "Extra Edition", but to no avail.
Many visual features of the game are sort of inside jokes; level and monster designs are drawn from previous Taito releases such as Arkanoid, Darius, and of course Bubble Bobble.