Looks like text color needs to change after the theme color changes the background.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/7a0c954204c16fc4e7ef3298bb037eac28506fde

commit 7a0c954204c16fc4e7ef3298bb037eac28506fde
Author: Rouslan Solomakhin <rouslan@chromium.org>
Date: Fri Apr 06 23:26:53 2018

[Payment Handler] Default text color without a theme.

Before this patch, a payment handler page without a theme would have a
white toolbar with white text on it, which was unreadable.

This patch checks for a theme background color of zero, which indicates
absence of a theme, and uses the default text color in this case.

After this patch, a payment handler page without a theme has white
toolbar with black text on it, which is readable.

Bug:  829973 
Change-Id: I5b87baac7c46cc4e087d4b61c2c8e4a4ea432df8
Reviewed-on: https://chromium-review.googlesource.com/1000319
Reviewed-by: anthonyvd <anthonyvd@chromium.org>
Commit-Queue: Rouslan Solomakhin <rouslan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#548964}
[modify] https://crrev.com/7a0c954204c16fc4e7ef3298bb037eac28506fde/chrome/browser/ui/views/payments/payment_request_views_util.cc

Tested the issue on chrome version# 67.0.3390(build without fix) using Mac 10.12.6 with steps mentioned below:
1) Launched chrome version# 67.0.3390.0(build without fix) and chrome version# 67.0.3393.0(build with fix) and navigated to URL: https://badssl.com
2) Checked the behaviour by zooming in and out the page, didn't observed any white space in both the builds

@Rouslan Solomakhin: Please find the screen cast of both the builds(67.0.3390.0 & 67.0.3393.0) for your reference and help us in verifying the fix.

Thanks!

Deleted: 829973 - 67.0.3390.0.mp4 1.8 MB

	829973 - 67.0.3390.0.mp4 1.8 MB View Download

Deleted: 829973 - 67.0.3393.0.mp4 2.0 MB

	829973 - 67.0.3393.0.mp4 2.0 MB View Download

Very sorry for bad communication on my part. Please see the attached videos for the steps to reproduce instead.

Deleted: 67.0.3386.1.ogv 5.3 MB

	67.0.3386.1.ogv 5.3 MB View Download

Deleted: 67.0.3394.0.ogv 6.6 MB

	67.0.3394.0.ogv 6.6 MB View Download