The clue label (the set of numbers at the edge of a row or column) for a line will change color when the squares filled on that line satisfy the clue.
Important: Please note that this indicates that the blocks of filled squares entered on the line are a valid answer, but not necessarily the correct answer to complete the puzzle.
The purpose of this highlighting feature is to help the player keep track of lines that they have already solved, so that they can focus on the remaining unfinished lines.
The reason that the highlighting does not only occur for the correct answer is that this would make many puzzles trivially easy to complete by trial and error.
Remember: you should never need to use guesswork to solve a Picture Cross puzzle. Please refer to the "How to play Picture Cross" and "Strategy Guide" sections of this FAQ to learn more about the techniques you can use to logically solve puzzles.
The purpose of this highlighting feature is to help the player keep track of lines that they have already solved, so that they can focus on the remaining unfinished lines.
The reason that the highlighting does not only occur for the correct answer is that this would make many puzzles trivially easy to complete by trial and error.
Remember: you should never need to use guesswork to solve a Picture Cross puzzle. Please refer to the "How to play Picture Cross" and "Strategy Guide" sections of this FAQ to learn more about the techniques you can use to logically solve puzzles.