Want to change description text color

div#tab-description {
    color: #2f4668;
}

To add or override CSS: use the “Additional CSS” option in the customizer. https://www.ads-software.com/support/article/appearance-customize-screen/

Learn to use the Chrome Developer Tools or Firefox Developer Tools to help you see and test changes to your CSS.

In addition to that, I suggest you to take a look at the theme’s documentation:

https://docs.drfuri.com/martfury/2-how-to-change-color-scheme/