How to get them ? Simply click on show candidates in the left column of your sudoku page. Green cells indicate nacked singles (just one candidate) while red cells indicate an error with your sudoku (no candidate).
In the bottom of the left column of your sudoku page, click on the color selector (where 8C90FF is written) and choose your favourite color as in the image below. Then click apply. Its done! You do not want the proposed default gradient ? Click on "no gradient". Here is your personal page sudoku. Enjoy ! To return to the original color click on "initial color".
In the left column of your sudoku, you can now change the colors of your grids. An overview of new possibilities below : blue and blue, black and gray, black and blue, pink and blue, inverted blue or the home version. Enjoy !