Hello,
There is a call in the index.php that applies that color selection to multiple elements including the active top menu color.
#s5_nav li.active a, .module_round_box .s5_h3_first, .module_round_box-darkgray2 .s5_mod_h3_outer h3 .s5_h3_first, .module_round_box-darkgray .s5_mod_h3_outer h3 .s5_h3_first, .s5_pricetable_column.recommended .button, a {
color: #db25db;
}
However, I would double check that you used a !important call properly as this should override the above rule since it doesn't have a !important value attached to it.
#s5_nav li.active a {
color: #ff0000 !important;}
Should always outweigh the index.php value so I would double check that the coding was added properly and the cache was cleared as well after making the changes. I tested the coding I gave you on my copy and it was working as an override properly.
If you still have issues you can remove the active menu call from the index.php line I referenced above and manually add it into the CSS file with a color code.
Regards,