Themes

It's probably controlled in styles.php rather than config.php.
Where did you get the OSX blue theme? I've never heard of it.

In styles.php edit the class called .feedbacktext. In (all/most???) themes this is actually controlled by config.php - it uses cellheading2. So presumably your cellheading2 is set to light grey.

However, I wouldn't recommend editing cellheading2 - this will change all the instances of it (i.e. when it is used for background colours for table headings).

Instead simply get rid of the link to cellheading2.

Perhaps your styles.php says this:

.feedbacktext {
color: <?PHP echo $THEME->cellheading2?>;
}

change that to whatever colour you want, e.g.

.feedbacktext {
color: #333333;
}

for a darker grey or

.feedbacktext {
color: #ff0000;
}

for bright red.

cheers