Painter Smurf can paint objects blue, red, and white. Unlock his other colors by completing the corresponding imgage at the Painter Smurf's mini-game at a "Close To Perfection" rank. Note - Colors cannot be unlocked in Practice mode.
If you don't want to wait for crops to grow, head to the Settings menu and select "General." Now, choose "Date and Time" and turn off "Set Automatically" and then change the time for your crops manually. Note: You can get away with this exploit about 20 times before some Smurfs leave.
The game automatically saves the village every day. If you want to revert to a previous day or lost your village somehow, use the following hidden feature: Start the game, choose Options from the main menu, and tap Papa Smurf 16 times (not the "Restart Game" feature next to his icon). After the 16th time a new option will be available in the bottom right corner called "Recover Village". Select it to find a list of saved games.