There are currently no options built into the planetkde.org site that would allow visually impaired users to use a dark theme. This can easily be achieved with css to provide the choice for users to opt into a dark theme. 

Fully-functional code (changing the background to dark grey) to provide this feature is listed below the break ; 

--

@namespace url(http://www.w3.org/1999/xhtml);
/*text&background*/

html,
body,
tbody,
thead,
th,
tr,
td,
blockquote,
li,
ul,
h1,
h2,
h3,
h4,
h5,
h6,
font,
strong,
p,
form,
footer {
    color: white !important;
    background: #272B30 !important;
}
select,
button {
    background: #272B30 !important;
}
div,
span,
a {
    background-color: #272B30 !important;
}
select,
input,
span,
code,
textarea,
pre,
label,
div,
dd,
option {
    color: white !important;
}
/*links*/

a {
    color: grey !important;
}
a:visited {
    color: #224375 !important;
}
/*highlight*/

textarea,
pre,
input,
code {
    background: grey !important;
}

--

Bug submission was requested after an enquiry to the PlanetKDE webmaster was responded to by Albert Astals Cid.