Hi Delma,
Now we don’t have customizer setting to change bottom widgets title color, but we will soon make it available on next update. So for now you can use following css to fix your issue:
#bottom-wrapper .widget-title {
color: #eeee22 !important ;
}
You can change value of color Property as per your requirement, [For Reference : http://www.w3schools.com/cssref/css_colors.asp ].
Note: Please use custom css plugin or child theme to write css, otherwise your changes will lost on theme update.
Thanks