This coloring page is all about the Slytherin House. Silver and green are the colors associated with this House, and that is the color scheme for this image. The shield is divided into four sections, two of which are silver, and the other two green. In the center of the shield, there is a silver and green snake winding from the top left to the bottom right. Above the shield, the green and silver banner displays the brave message: "Slytherin Will Prevail."
For this coloring page, I would suggest starting with a light green base color to represent the tone of the Slytherin House. Use a darker green to color in the top right and bottom left sections of the shield, in order to provide a contrast between the silver elements. To color in the snake, use a slightly different shade of silver to make its scales stand out, and use a bright olive green for its eyes. As for the banner, use a dark silver for the lettering, and either a very light green or a shimmery silver for the background.