It is true that the default LED colour on the Priv is white. And it is true that in the Settings>Sound&Notifications>App Notifications> menu, the LED colours can only be changed for certain Google apps. If you want *at least* your email LEDs to show up as red (i.e, Gmail, Exchange AS....), you can change the colours only through the Hub settings (Hub Settings>Accounts>(Pick Account)>Notification Light Colour).
Hope this helps!
AW