The micro computer legend Andrew Braybrook wrote a great piece about Rainbow Islands and its home conversion in '89. These ports were excellent and pretty close to the arcade original, the development came with a few surprises.
The full article is a great read, lots of insight. It can be found here: https://uridiumauthor.blogspot.com/2018/03/rainbow-islands.html
We agreed to do the job, for a fixed sum, based on getting the arcade machine and source graphics and documentation from Taito. The job, we reckoned, would take about 9 months and milestones were assigned, based on our knowledge of the game and that it showed 7 islands on the start screen.
One Friday night we got David to play the game the whole way through. [...] By this time we had discovered that the game had a "bad" ending after island 7, i.e. well done but you didn`t do it quite right. We needed that on video too, so he played it wrong, then followed the advice given in the ending to play it right. Imagine our surprise then when he got to the end of island 7 and 3 more secret islands rose up out of the water. We were expecting just a different ending.
The full article is a great read, lots of insight. It can be found here: https://uridiumauthor.blogspot.com/2018/03/rainbow-islands.html