Hi!
When using Emacs in a terminal that supports 256 colors (such as the built-in terminal on macOS), the faces diff-added and diff-removed look the same.
They are defined to have a background color of #eeffee and #ffeeee, respectively, in light background mode. When a diff is viewed in a terminal, they are both rendered using light grey background, so it's impossible to distinguish between them.
In Emac 26, they were defined using #ddffdd and #ffdddd, respectively, which is rendered fine in the terminal (on both Emacs 26 and 27).
One way to solve this is to add alternative color definitions using the "min-colors" requirement. Another is to go back to the old values.
-- Anders Lindgren
In GNU Emacs 27.0.50 (build 1, x86_64-apple-darwin16.7.0, NS appkit-1504.83 Version 10.12.6 (Build 16G29))
of 2019-05-01 built on mbp.lan
Repository revision: 7dafbe3ab91e838803a84ab388bca03ff985e312
Repository branch: master
System Description: Mac OS X 10.12.6
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