Accessing global variable in “CSS” (style.php)

I'm doing a style.php CSS file so I can use some dynamic variables in the CSS within a Wordpress installation:

<?php header("Content-type: text/css"); ?>

and so on.

How can I access a global variable from within the style.php file or pass a variable to it?

The code I'm trying to get to work within the CSS is like

$maincolor = $cap->br_main_color;

Also:

• Ignore the caching issue. This is just a personal project.
• Passing the variable in the link to the stylesheet is too complex for this (in my opinion).

EDIT: As a bit more explanation: What I'm doing is generating an entire theme based of a number of colors and calculating shades for hover effects etc. Roughly 50% of the styles have some PHP within them. Everything works just fine if I manually input colors to style.php but I'm trying to make it even simpler for less tech-savvy people and use a color picker.