Set default text colour for Settings tabs

res/css/views/settings/tabs/_SettingsTab.scss

@@ -14,6 +14,10 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
+.mx_SettingsTab {
+    color: $muted-fg-color;
+}
+
 .mx_SettingsTab_warningText {
     color: $warning-color;
 }