colors change is very easy with the power of scss variables. Open source/scss/variables.scss file in a text editor. Then you can see the global variables we used in this theme. primary-color defines the theme default color. If you change it the whole theme default colors will be changed when you compile the theme again. You can also change the other variable colors like this.
// Color Variables
$primary-color: #757fe6;
$text-color: #333;
$body-color: #fff;
$border-color: #E2E2E2;