One improvement that certainly comes to mind is use of pictures instead of colors, as shown in the Using images screenshot. How difficult would that be? It turns out that this is surprisingly easy because we already have the game logic firmly in place!

In the images folder, we supply a number of game pictures. Instead of the color property we give the cell a String property (image), which will contain the name of the picture file. We replace util\color.dart with util\images.dart, which contains a variable imageList with the image filenames. In util\random.dart, we replace the color methods with the following code:

String randomImage() => randomListElement(imageList); 

The changes to memory.dart are also straightforward: replace the usedColor list with List usedImages = []; and the method _getFreeRandomColor with _getFreeRandomImage, which uses the new list and method:

List usedImages...