How can I change the color of the text in the footer section?

Hello Tunc ! 
If you want to change the color in the footer section of the DW Focus theme, you can do as the following: 
1. Install the Jetpack by WordPress.com plugin.
2. Setting Jetpack then enable the Custom CSS feature.
3. Move through Appearance > Editor Css, add the following code:

   #colophon.dark a {
    color: #FFF;
}
#colophon.dark #site-tools .footer-toggle:after {
    border-color: #FFF;
    color: #FFF;
}
#colophon.dark {
    color: #FFF;
}
#colophon.dark .input-append input[type="text"] {
    color: #FFF;
}

Hope this helps !