Collecting all of the gems in the correct order of color (from left to right on the gem counter - RED, ORANGE, YELLOW, GREEN, LIGHT BLUE, DARK BLUE, and MAUVE) not only awards you the life and Bonus Gem, it also grants you access to a magical secret room. When you reach the end of the level, a silver door appears. You don't have to fight the Boss.
On the fifth island you'll find a box in the secret room which you should collect. There's also a gate with a '7' on it, leading to island 7.
Even more useful is how to create any color gem. The screen is split into several invisible vertical stripes of color. When a gem falls, its color is determined by the `color' of the area into which it fell. Now all you have to do is guage ca refully where the dead enemy will fall to create the gem color of your choice.
Type one of the following on the title screen, while the rainbow is cycling through colors:
"BLRBJSBJ"----------------Permanent fast shoes
"RJSBJSBR"-----------Permanent double rainbows
"SSSLLRRS"-------------Permanent fast rainbows
"BJBJBJRS"------------------------------Hint a
"LJLSLBLS"------------------------------Hint b
"LBSJRLJL"----------Continue after island five
"RRLLBBJS"--All hidden food becomes money bags
"RRRRSBSJ"-------Does both of the previous two
"SRBJSLSB"-------Gives you 100 million counter
Visit the Bub and Bob home page . The site has everything about the game Bubble Bobble and its derivitives, including Rainbow Islands.