Able to reproduce this issue on 67.0.3379.0 and on latest canary 67.0.3381.0 using Windows 10, Mac 10.12.6 and Ubuntu 14.04. As the issue is seen from M-60(60.0.3112.0). Hence considering this issue as Non-Regression and marking as Untriaged.

Thanks!

Thanks for the report!  I agree with having white arrows for better contrast, we use white on blue in checkboxes/icons on selected menu-items as well, so this will be consistent.

We'd totally welcome contributed patches!  If you haven't already seen it, there's a contribution guide (bit.ly/devtools-contribution-guide) on how to get started.  It's a bit long, but feel free to ask questions along the way.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/7bff7b347b28cf5205d84abbc1a6d2a69af5e78b

commit 7bff7b347b28cf5205d84abbc1a6d2a69af5e78b
Author: Erik Luo <luoe@chromium.org>
Date: Mon Jun 25 23:05:29 2018

DevTools: force arrows in SoftContextMenu to be white

Screenshot: https://imgur.com/a/cN62iYX

Bug:  825535 
Change-Id: If5ddf68061430539e9a2e69194bb58071bff3bdc
Reviewed-on: https://chromium-review.googlesource.com/1112844
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Commit-Queue: Erik Luo <luoe@chromium.org>
Cr-Commit-Position: refs/heads/master@{#570218}
[modify] https://crrev.com/7bff7b347b28cf5205d84abbc1a6d2a69af5e78b/third_party/blink/renderer/devtools/front_end/ui/softContextMenu.css

Able to reproduce the issue on chrome reported version 67.0.3379.0
Verified the fix on Mac 10.12.6, Windows-10 & Ubuntu 14.04 on Chrome version #69.0.3473.0 as per the comment#0
Attaching screenshot for reference.
Observed "Arrow icon changed to white to match the text changing to white"
Hence, the fix is working as expected.
Adding the verified label.

Thanks!

While this bug is fixed, there are still many good first bugs.  "Hotlist-Goodfirstbug" is one label to look for.