Disabled `ion-datetime` label's color differs from disbaled `ion-input`' label's color.

[ionitron-bot]

Original issue by @Kopleman on 2017-05-10T10:31:01Z

Ionic version: (check one with "x")
[ ] 1.x
[ ] 2.x
[X] 3.x

I'm submitting a ... (check one with "x")
[X] bug report
[ ] feature request
[ ] support request => Please do not submit support requests here, use one of these channels: https://forum.ionicframework.com/ or http://ionicworldwide.herokuapp.com/

Current behavior:
Disabled ion-datetime label's color differs from disbaled ion-input' label's color. ion-datetime label's color has opacity that other inputs dont

Expected behavior:
Same styles for all input types

Steps to reproduce:
http://embed.plnkr.co/YYcnxbsuwhMX9tXYW4Qn/

Related code:

<ion-content>
  <ion-row>
      <ion-col>
        <ion-item >
            <ion-label>lifeTime</ion-label>
            <ion-input name="lifeTime" type="number" 
                       [disabled]="true"
                       >
            </ion-input>
          </ion-item>  
      </ion-col>
      <ion-col>
        <ion-item>
            <ion-label>From</ion-label>
            <ion-datetime displayFormat="DD/MM/YYYY HH:mm"
                           name="hotTimeEnd" [disabled]="true"
                          ></ion-datetime>
          </ion-item>
      </ion-col>
    </ion-row>     
</ion-content>

Other information:

Ionic info: (run ionic info from a terminal/cmd prompt and paste output below):

Your system information:

Cordova CLI: 6.5.0
Ionic Framework Version: 3.0.1
Ionic CLI Version: 2.2.3
Ionic App Lib Version: 2.2.1
Ionic App Scripts Version: 1.3.0
ios-deploy version: Not installed
ios-sim version: Not installed
OS: Windows 10
Node Version: v6.9.2
Xcode version: Not installed