If you are using a DotNetNuke skin that has set the body background color to a dark color (e.g. black), then when you use the FCK HTML Editor, select an image and then Browse Server, the popup window inherits the skin body color.

To fix this kind of problem, right-click on the problem window, View Source and see what CSS file might be specific to this popup. Then edit this CSS file with a different background color.

For example, I found "/Providers/HtmlEditorProviders/Fck/FCKtemplates/imageBrowser/Default/Styles.css" and added the lines:

/* customization for skin with black background */
body
{
    background-color: White;
}

This solved the problem!