Chrome 63.0.3208.0 (Official Build) canary (64-bit) (cohort: 64-Bit)
Windows 10 Enterprise Version 10.0.14393 Build 14393

I am able to repro this issue. 

Screenshot of close x and text on screen:
https://screenshot.googleplex.com/5Wus1PpV1Fv.png

Close X:
Foreground:#A6A6A6
Background:#FFFFFF
The contrast ratio is: 2.4:1

Text such as "Speak Now":
Foreground:#737373
Background:#FFFFFF
The contrast ratio is: 4.7:1

No mic icon on ChromeOS Version 62.0.3201.0 (Official Build) canary (64-bit)

The low contrast should be an easy fix.

It's weird that the microphone doesn't show up on CrOS; it should be there on all platforms. It's possible that you're seeing the local NTP, which doesn't have voice search yet. You can check that by doing right-click->"View page source", and then looking at the URL in the omnibox. If it looks like "chrome-search://local-ntp/local-ntp.html", then you're seeing the local NTP. (For the remote one, the URL looks like "https://www.google.com/_/chrome/newtab".)

Friendly ping - any idea who can help with these contrast adjustments? 

I can implement the change once we've decided on what color we want. I don't know who can/should make that decision.

re: c#4, 

Let's use

54% of Black (or #757575) - this makes the contrast 4.6:1.

Thanks!

I'll handle this.
Turns out it's already #777, but 0.6 opacity...

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/42e15918dbba49cb3e14390837ce2926d0195ce3

commit 42e15918dbba49cb3e14390837ce2926d0195ce3
Author: Marc Treib <treib@chromium.org>
Date: Tue Nov 28 20:22:53 2017

Local NTP Voice: Fix contrast ratio on 'x' button

This makes the button a bit darker so it meets the minimum contrast ratio

Bug:  707004 
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I8160d6ba4bead047064b6cc1b2de2c56ffea6c23
Reviewed-on: https://chromium-review.googlesource.com/793815
Reviewed-by: Chris Pickel <sfiera@chromium.org>
Commit-Queue: Marc Treib <treib@chromium.org>
Cr-Commit-Position: refs/heads/master@{#519817}
[modify] https://crrev.com/42e15918dbba49cb3e14390837ce2926d0195ce3/chrome/browser/resources/local_ntp/voice.css

Fixed for the local NTP. To test:
Enable
chrome://flags/#use-google-local-ntp
and
chrome://flags/#voice-search-on-local-ntp
and restart Chrome as prompted, then open an NTP normally.

Tested the issue on Mac 10.12.6, Windows 10 and Ubuntu 14.04 using Chrome version M64 - 64.0.3280.0 by following the below steps:

1. Enable flags: chrome://flags/#use-google-local-ntp and chrome://flags/#voice-search-on-local-ntp
2. Relaunched browser.
3. Open a new tab page.
4. Tab to Mic icon and performed key board action Enter/Return.
5. Using Dev tools inspected the 'X' button.

Observed the below observations (attached screenshot for reference):
1. opacity: .54;
2. Color: black;

@treib -- Could you please confirm whether the observed values are intended or not.

Thanks in advance.

Deleted: 707004.png 200 KB

	707004.png 200 KB View Download

Yup, that's exactly as intended, thanks!

Adding the labels TE-Verified-M64 and TE-Verified-64.0.3280.0 as it is working as intended. 

Google Chrome 65.0.3325.2 (Official Build) canary (64-bit) (cohort: Clang-64)

Excellent, resolving.

Foreground:#757575
Background:#FFFFFF

The contrast ratio is: 4.6:1