Change colour navbar header Ionic 2

Question

I have this problem... My colour is white right now, my code is like this:

<ion-header >
  <ion-navbar>
    <ion-title>
      HELLO
    </ion-title>
  </ion-navbar>
</ion-header>

Change color with this opcion is easy (primary, secondary, danger, light, dark)

<ion-header >
      <ion-navbar danger>
        <ion-title>
          HELLO
        </ion-title>
      </ion-navbar>
 </ion-header>

but my problem is when I want to use custom colors. Somebody know how can I resolve it? Thanks inadvance.

Best regards.