The Debian packaging of farbfeld is maintained in git, using the merging
workflow described in dgit-maint-merge(7). There isn't a patch queue
that can be represented as a quilt series.

A detailed breakdown of the changes is available from their canonical
representation - git commits in the packaging repository. For example,
to see the changes made by the Debian maintainer in the first upload of
upstream version 3, you could use:

    % git clone https://git.dgit.debian.org/farbfeld
    % cd farbfeld
    % git log --oneline 3..debian/3-1 -- . ':!debian'

(If you have dgit, use `dgit clone farbfeld`, rather than plain `git
clone`.)

A single combined diff, containing all the changes, follows.

--- farbfeld-3.orig/2ff
+++ farbfeld-3/2ff
@@ -25,6 +25,12 @@ else
 		jpg2ff < "$TMP"
 		;;
 	*)
+		if [ ! -x /usr/bin/convert ] ; then
+			printf "%s: cant convert from %s -- missing \`convert' program" "$0" "$FORMAT" >&2
+			printf "Run \`apt install imagemagick' to install it" >&2
+			exit 1
+		fi
+
 		convert "$TMP" png:- | png2ff
 		;;
 	esac
--- farbfeld-3.orig/config.mk
+++ farbfeld-3/config.mk
@@ -4,13 +4,13 @@ VERSION = 3
 # Customize below to fit your system
 
 # paths
-PREFIX = /usr/local
-MANPREFIX = ${PREFIX}/man
+PREFIX = /usr
+MANPREFIX = ${PREFIX}/share/man
 
 # flags
-CPPFLAGS = -D_DEFAULT_SOURCE
-CFLAGS   = -std=c99 -pedantic -Wall -Wextra -Os
-LDFLAGS  = -s
+CPPFLAGS += -D_DEFAULT_SOURCE
+CFLAGS   += -std=c99 -pedantic -Wall -Wextra -Os
+LDFLAGS  += -s
 PNG-LDFLAGS = -lpng
 JPG-LDFLAGS = -ljpeg