Here some main rules:
1. Two primary color (e.g blue and yellow) will give you a secondary color (green).
2. But not like in real life, you will take a primary color back if you will mix secondary and primary colors (In real life you will have some dark brown color from this mix).
3. When you move any drop, other drops with the same color will move the same way.
4. Freed cells will be filled with color drops that was chosen by pattern.

If you have any difficulties with colors you can use an option to add digits (1 to 3) inside a drops. The rules stays the same. 1 and 2 represents primary colors and 3 is like a secondary color. So 1 + 2 = 3, and 3 - 2 = 1.