Chrome Version : 67.0.3381.0 (Official Build) ae7ce2710f11dd78c2f787b888d2cc19b912bf49-refs/heads/master@{#545918} 32/64-bit
OS : Windows(7,8,8.1,10), Mac(10.12.6, 10.13.1, 10.13.4)

What steps will reproduce the problem?
1. Launch chrome, open devtools on NTP and click on 'Toggle device toolbar' icon.
2. Hit F1 key to open 'Preferences' and change theme to 'Dark'.
3. Observe the color of 'Toggle device toolbar' icon.

Actual Result : Color of 'Toggle device toolbar' icon appears faint in 'Dark' theme mode.

Expected Result : 'Toggle device toolbar' icon should have slighty dark color such that icon is easily visible in Dark theme mode.

This is a regression issue, broken in M-67 and providing the bisect using per-revision script:
Good Build : 67.0.3378.0 (Revision : 544932)
Bad Build : 67.0.3379.0 (Revision : 545319)

You are probably looking for a change made after 544943 (known good), but no later than 544944 (first known bad).

CHANGE-LOG URL:
https://chromium.googlesource.com/chromium/src/+log/d3d494cbde1898d53f228ea5ce8ff8e3143bbc91..c4b54ebcabb606f7bd8caa8df7e55c331be6232b

Suspect : https://chromium.googlesource.com/chromium/src/+/c4b54ebcabb606f7bd8caa8df7e55c331be6232b

@Pavel : Could you please check whether this is caused with respect to your change, if not please help us in assigning it to the right owner.

Note : 
1. This issue is not observed on Linux(14.04 LTS) OS since the color is proper and icon is easily visible even in Dark theme mode in Linux OS.
 

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