In Customizer:

Footer > Footer Content

<br><br>
     <i class="fa fa-wheelchair" aria-hidden="true"></i> Accessible Colors<br><br>
    <button class="dfg-contrast">
    Adjust Color Contrast
    </button>
    <button class="dfg-reset">
    Reset Color
    </button>
<br><br>

===

Custom > Edit Global CSS

.dfg-change {
  background: #d4d4d4 !important;
}

.dfg-change-wht {
  background: #ffffff !important;
}

.dfg-change-txt {  
  color: #000000 !important;
}

.dfg-change-txt-wht {
  color: #ffffff !important;
}

.dfg-no-img {
  display: none !important;
}

.dfg-yes-img {
  display: inherit !important;
}  

===

Custom > Edit Global Javascript

(function($){
  
$("button.dfg-contrast").click(function () {
        $("body, div.x-section").addClass("dfg-change-wht");
        $("div.x-topbar, p.p-info, div.x-navbar, .x-btn, .x-btn-navbar, footer, .x-creative-cta").addClass("dfg-change");
        $("p, a, h1, h2, h3, h4, h5, h6, footer, div.x-text, div.x-raw-content, div.x-accordion-group, div.df-left-nav-widget, div.number-wrap.w-h. span.text-below").addClass("dfg-change-txt");
        $(".tg-item-title a").addClass("dfg-change-txt-wht");
        $("div.dfg-title").addClass("dfg-change-txt");
        $("div.dfg-item").addClass("dfg-change");
        $("div.dfg-item img, div.backstretch img").addClass("dfg-no-img");
        $("div.dfg-item.logo, div.dfg-slider").removeClass("dfg-change");
        $("div.dfg-item.logo img, div.dfg-slider img").addClass("dfg-yes-img");
        setCookie("accessible", "on", 60);
    });
    $("button.dfg-reset").click(function () {  
        $("body, div.x-section").removeClass("dfg-change-wht");
        $("div.x-topbar, p.p-info, div.x-navbar, .x-btn, .x-btn-navbar, footer, .x-creative-cta").removeClass("dfg-change");  
        $("p, a, h1, h2, h3, h4, h5, h6, footer, div.x-text, div.x-raw-content, div.x-accordion-group, div.df-left-nav-widget, , div.number-wrap.w-h. span.text-below").removeClass("dfg-change-txt");        
        $(".tg-item-title a").removeClass("dfg-change-txt-wht");
        $("div.dfg-title").removeClass("dfg-change-txt");
        $("div.dfg-item").removeClass("dfg-change");    
        $("div.dfg-item img, div.backstretch img").removeClass("dfg-no-img");
        setCookie("accessible", "off", 60);
    });
 

        function setCookie(cname, cvalue, exminutes) {
            var d = new Date();
            d.setTime(d.getTime() + (exminutes*60*1000)); // exminutes must be set to number of minutes cookie will be valid
            var expires = "expires="+ d.toUTCString();
            document.cookie = cname + "=" + cvalue + ";" + expires + ";path=/";
        }

        function getCookie(cname) {
            var name = cname + "=";
            var decodedCookie = decodeURIComponent(document.cookie);
            var ca = decodedCookie.split(';');
            for(var i = 0; i <ca.length; i++) {
                var c = ca[i];
                while (c.charAt(0) == ' ') {
                    c = c.substring(1);
                }
                if (c.indexOf(name) == 0) {
                    return c.substring(name.length, c.length);
                }
            }
            return "";
        }

        function checkCookie(cookie_name) {
            var accessible = getCookie(cookie_name);
            if (accessible == "") {
                setCookie("accessible", "off", 60); //set cookie validity to one hour (60 minutes)
            } else if (accessible == "on") {
                $("button.dfg-contrast").click();
            } else {
                $("button.dfg-reset").click();
            }
        }
  
    checkCookie("accessible");

        function getCookie(cname) {
            var name = cname + "=";
            var decodedCookie = decodeURIComponent(document.cookie);
            var ca = decodedCookie.split(';');
            for(var i = 0; i <ca.length; i++) {
                var c = ca[i];
                while (c.charAt(0) == ' ') {
                    c = c.substring(1);
                }
                if (c.indexOf(name) == 0) {
                    return c.substring(name.length, c.length);
                }
            }
            return "";
        }
        
    if(getCookie("accessible")=="on") jQuery("div.dfg-item img, div.backstretch img").addClass("dfg-no-img");
  
})(jQuery)

===

DF Grid Plus Plugin Change

Added class of "logo" to //display logo section in Grid df-grid-builder.php file.

//display logo
if (get_row_layout() == 'logo_grid_item'):
    $dfg_logo_size     = get_sub_field('grid_item_logo_size');
$dfg_logo_upload   = get_sub_field('grid_item_logo_upload');
$dfg_logo_alt_tag   = get_sub_field('grid_item_logo_alt_tag');
$dfg_logo_position = get_sub_field('grid_item_logo_position');
$dfg_logo_shape = get_sub_field('grid_item_logo_round_edges');
if (get_sub_field('grid_item_logo_size') == 'dfg-logo'):
    echo '<div class="dfg-item logo ' . $dfg_logo_size . '"><img alt="' . $dfg_logo_alt_tag . '" class="' . $dfg_logo_shape . '" src="' . $dfg_logo_upload . '" /></div>';
endif;

if (get_sub_field('grid_item_logo_size') == 'dfg-2col-2row' || get_sub_field('grid_item_logo_size') == 'dfg-2col-3row'):
    echo '<div class="dfg-item logo ' . $dfg_logo_size . ' ' . $dfg_logo_position . '"><img alt="' . $dfg_logo_alt_tag . '" class="' . $dfg_logo_shape . '" src="' . $dfg_logo_upload . '" /></div>';
endif;
endif;
//END display logo


===

Other Dependencies

- In child theme CSS files, remove !important attribute from text and background properties
- Remove #f2f2f2 from left nav widget  in WP Admin
- In child theme CSS add #df-tb-color ID. Then wrap topbar content in Customizer with this ID.