The objective is to get the rainbow as shown below in a limited number of steps from the initial state. If you succeed you win the prize for that contest. Each purchased app contributes 50% of the net price* to the prize fund. So the more apps are purchased, the bigger the fund; the bigger the fund, the bigger the prizes. Spread the word, mike it viral, solve one of the contests, and make a fortune :)
IMPORTANT: Only apps purchased in Google Play Store are eligible for competition.
Every time a tile is pressed its color changes to the next rainbow color (from yellow to violet). To make it difficult, four different tiles are changed by the app for each press you make. The number of available steps you have left is shown below the tiles. You can reverse your moves by pressing the 
button or return to the beginning by pressing the 
button. To choose a different contest press the 
button.
There are 5 levels, A to E; A is the toughest, E the easiest. The only difference is in the number of steps required for the solution. Level A has 16 steps (hence the app name, Sixteen). Each successive level requires one step less and therefore has fewer possible combinations.
There is a single A-level contest, and then 2, 5, 10, and 100 contests for each successive level.
Each level is allocated one fifth of the total prize fund. Since the number of contests increases with each level, the prize for each contest decreases correspondingly. The prize currently available for a particular contest is shown above the tiles.
If you solve a contest you'll be asked for contact data (email or phone number) so that payment can be arranged. Note that it doesn't matter when you solve the contest, you will always get the total amount for that contest once all the contests are closed. So the bigger the final fund, the bigger your prize.
* Net price is the price after tax and Play Store fee (30%) were deducted. For example, if the app price is €1 + VAT then net price will be €0.70 and the prize fund contribution will be €0.35.