I went through all of the packets exchanged between cups and the printer during a print job, and found that there was no indication from the printer that it didn't support color printing.

The printer actually continuously advertises that it supports color printing during the initial setup, as well as during status updated while the print job is ongoing.

I think we should try to contact Epson about this because there doesn't seem to be any obvious issue on our end.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/096104a007d3bf56d3703f26e537635b1c6e5bb7

commit 096104a007d3bf56d3703f26e537635b1c6e5bb7
Author: David Valleau <valleau@chromium.org>
Date: Tue Aug 14 09:13:38 2018

Adding patch to allow PWG Raster types to vary by case

This change adds a patch to CUPS which fixes an issue where Epson
printers would always print in black and white when provided with
pwg-raster, even if the requested print was in colour.

Their reported color scheme was not recognized by CUPS, causing
them to default to black and white.

BUG= chromium:870099 ,  chromium:804990 
TEST=Tested Manually on device

Change-Id: I67473fa41a3a201e6e59312ec17669d8e34bb35a
Reviewed-on: https://chromium-review.googlesource.com/1170082
Commit-Ready: David Valleau <valleau@chromium.org>
Tested-by: David Valleau <valleau@chromium.org>
Reviewed-by: Sean Kau <skau@chromium.org>

[modify] https://crrev.com/096104a007d3bf56d3703f26e537635b1c6e5bb7/net-print/cups/cups-2.1.4.ebuild
[rename] https://crrev.com/096104a007d3bf56d3703f26e537635b1c6e5bb7/net-print/cups/cups-2.1.4-r51.ebuild
[add] https://crrev.com/096104a007d3bf56d3703f26e537635b1c6e5bb7/net-print/cups/files/cups-2.2.4-case-insensitive-pwg-raster-types.patch

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/third_party/cups/+/c0bcf741d3630f0fd6d092fc2b9ec73a12a50603

commit c0bcf741d3630f0fd6d092fc2b9ec73a12a50603
Author: David Valleau <valleau@chromium.org>
Date: Thu Aug 16 07:30:04 2018

Allow PWG Raster types to vary by case

BUG= chromium:87099 ,  chromium:804990 
TEST=None

Link to the upstream patch:
https://github.com/apple/cups/commit/d2817c9f02391c8cba8ae478b952d3405f45ff59

Change-Id: Iea759511ef8e5f7e7aa865a2838da8813a3fb5c4
Signed-off-by: David Valleau <valleau@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1174954
Reviewed-by: Sean Kau <skau@chromium.org>

[modify] https://crrev.com/c0bcf741d3630f0fd6d092fc2b9ec73a12a50603/cups/ppd-cache.c