The color for your buttons comes from the btn-x classes (e.g., btn-primary, btn-success), so if you want to manually change the colors by writing your own custom css rules, you'll need to change:
/*This is modifying the btn-primary colors but you could create your own .btn-something class as well*/
.btn-primary {
color: #fff;
background-color: #0495c9;
border-color: #357ebd; /*set the color you want here*/
}
.btn-primary:hover, .btn-primary:focus, .btn-primary:active, .btn-primary.active, .open>.dropdown-toggle.btn-primary {
color: #fff;
background-color: #00b3db;
border-color: #285e8e; /*set the color you want here*/
}