Look at the tiny squares on top. The first 5 are: red, blue, yellow, green, yellow. Now look at the big grid. See those red squares that are outlined? You do NOT have to start your sequence in them. However, those two must be red.
There are 162 puzzle levels. They start out very simple with 2x2 grids. Some of the 3x3 grids get tough. There are 2 other modes in the game. Look at the second image. See the arrow? When you pass over that square, your next move is up. See the yellow/pink curved arrows? That means that when you pass over that square, the pink & yellow outlined squares will switch to the other.
At first, I thought that the Curved Arrows mode was a gimmick just to remember that to do the opposite. However, some of the puzzles have multiple Curved Arrows like this: blue/yellow and yellow/red. In this situation, a red could become just a yellow, and it could then become a blue - depending on the sequence. Extremely hard.
Each puzzle can be solved with a hint: if you choose, the first and last square will be revealed.
I really like Stroke! Stroke! is definitely one of the Best Puzzle Apps of 2014.
For some reason, nobody is playing it. I guess the $.99 is just too prohibitive for some folks. The author is Ryo Takanezawa. He's got some other games too. Must investigate. Fortunately, they do not have titles like Heart Attack! or Cancer!
Read Nicola Salmoria's review