Change color levels

Changed the Emergency color because the background was the same color as the foreground.
And also changed the Alert and Critical colors to increase the contrast between these levels.

src/Monolog/Formatter/HtmlFormatter.php

@@ -30,9 +30,9 @@ class HtmlFormatter extends NormalizerFormatter
         Logger::NOTICE    => '#3a87ad',
         Logger::WARNING   => '#c09853',
         Logger::ERROR     => '#f0ad4e',
-        Logger::CRITICAL  => '#b94a48',
-        Logger::ALERT     => '#d9534f',
-        Logger::EMERGENCY => '#ffffff',
+        Logger::CRITICAL  => '#FF7708',
+        Logger::ALERT     => '#C12A19',
+        Logger::EMERGENCY => '#000000',
     );
 
     /**