Topic: Eddit the Shop sidebar menu style

Hello,

The active color you can change via Theme options > Styling > Main Color.

Regards

This white color comes from Main color in Theme Options http://prntscr.com/mxul0m same for this http://prntscr.com/mxullj White color, in this case, make elements invisible on your site because it is the same as the background color of the site.
Of course, you can add custom CSS code to change active color for current category in the sidebar:

.sidebar-widget ul li.current-cat>a {
    color: #cfd571;
}

but you have other elements that look a bit incorrect because of the white active color, so I would recommend you to change the active color via Theme Options instead of changing color for elements one by one via custom CSS code.

Regards