Does your blog site or website happen to use a very dark background color on which the PIWIK OptOut-Frame shall be displayed, reading the OptOut Text can get quite a bit difficult.
But if you change the font color of the OptOut-Frame in the appropriate template, reading the text gets a bit easier again.
Solution:
Open the file
..../piwik/plugins/CoreAdminHome/templates/optOut.tpl
and put in some CSS-Statements into the <body>-Tag .
This could look like
<bodystyle="font-size:12px;font-family: Helvetica; color:red; line-height:20px;margin:0;">
This little adaption changes the fontcolor of the OptOut-Text to red.