Confirming how portable this diff invocation is/isn't on any OS you can/want to install Nix on that isn't already in reports! This tries each diff on PATH, but I'm interested in default and common user-installed diffs (leave out any uncommon build you have). See 1st comment for a screenshot of expected output.

difftest.sh

#!/usr/bin/env bash

readonly ESC='\033[0m'
readonly GREEN='\033[32m'
readonly RED='\033[31m'

printf -v _UNCHANGED_GRP_FMT "%b" $'\033[2m%='"$ESC" # "dim"
# bold+invert+red and bold+invert+green just for the +/- below
# red/green foreground for rest of the line
printf -v _OLD_LINE_FMT "%b" $'\033[1;7;31m-'"$ESC ${RED}%L${ESC}"
printf -v _NEW_LINE_FMT "%b" $'\033[1;7;32m+'"$ESC ${GREEN}%L${ESC}"

for diff in $(type -ap diff); do
    $diff --unchanged-group-format="$_UNCHANGED_GRP_FMT" --old-line-format="$_OLD_LINE_FMT" --new-line-format="$_NEW_LINE_FMT" --unchanged-line-format="  %L" <(echo one && echo two && echo three) <(echo one && echo tow && echo three)
    echo "^^^ status: $? for $($diff --version | head -n 1) ($diff)"
done

reports

working
  macOS 10.14, 10.15, 10.16
    stock: (GNU diffutils) 2.8.1 (/usr/bin/diff)
    fink, homebrew, macports, pkgsrc: I haven't found an obvious bin/diff except the one in diffutils, which should be fine
  centOS 6
  
not working
  * nixpkgs plan9port/bin/diff (completely incompatible: diff [ -acefmnbwr ] file1 ... file2)

Expected output is something like: