How to change tab color in standard xerte template?

I'm building an XOT and using the Modern Sleek Gray template.
Within this template, the titles of the tabs are blue. How can you change this color?
What css code do i need to write to change this?

What page type are you using and referring to? Do you mean the background of a selected tab in a tab navigator is blue?
If so try:
.ui-state-active a, .ui-state-active a:link, .ui-state-active a:visited{
background:#F00000;
}
But learn how to use the browser tools to find the selector you need on a given page element e.g. right click and select inspect then look at the styles and explore changing values until you find what you need.
HTH
Ron