The colors used in the J1 Template come from Google’s Material Design (MD). The set has main colors and accent colors. You can use them for pictures or to make your own website brand colors. They are picked to look good together.
The color set begins with main colors and adds extra shades to give you a full set that works for both desktop and mobile websites on Android or iOS. Google suggests you use the 500 shade as your main color, and the other shades as accents that highlight your content for easier reading and better orientation.