It is preferable to configure the default theme via $mdThemingProvider. But, you can override Angular Material's default CSS classes to achieve your desired result.
Tab's background color
md-tabs > md-tabs-wrapper {
background-color: #f00 !important;
}
Tab's text color
md-tabs > md-tabs-wrapper > md-tabs-canvas > md-pagination-wrapper > md-tab-item:not([disabled]) {
color: #fff !important;
}
Active tab's text color
md-tabs > md-tabs-wrapper > md-tabs-canvas > md-pagination-wrapper > md-tab-item:not([disabled]).md-active, md-tabs > md-tabs-wrapper > md-tabs-canvas > md-pagination-wrapper > md-tab-item:not([disabled]).md-active md-icon, md-tabs.md-accent > md-tabs-wrapper > md-tabs-canvas > md-pagination-wrapper > md-tab-item:not([disabled]).md-active md-icon, md-tabs.md-default-theme.md-accent > md-tabs-wrapper > md-tabs-canvas > md-pagination-wrapper > md-tab-item:not([disabled]).md-focused, md-tabs.md-default-theme.md-accent > md-tabs-wrapper > md-tabs-canvas > md-pagination-wrapper > md-tab-item:not([disabled]).md-focused md-icon {
color: #222 !important;
}
Disabled tab's text color
md-tabs .md-tab[disabled], md-tabs .md-tab[disabled] md-icon {
color: #000 !important;
}
To configure via $mdThemingProvider, please refer Angular Material/$mdThemingProvider.
Hope it helps!