Index: usr.bin/diff/diff.h
===================================================================
--- usr.bin/diff/diff.h
+++ usr.bin/diff/diff.h
@@ -90,12 +90,13 @@
 	struct excludes *next;
 };
 
-extern int	lflag, Nflag, Pflag, rflag, sflag, Tflag, cflag, Wflag;
+extern int	lflag, Nflag, Pflag, rflag, sflag, Tflag, cflag, Wflag, colorflag;
 extern int	diff_format, diff_context, status, ignore_file_case;
 extern int	suppress_common;
 extern int	tabsize, width;
 extern char	*start, *ifdefname, *diffargs, *label[2], *ignore_pats;
 extern char	*group_format;
+extern const char	*add_code, *del_code;
 extern struct	stat stb1, stb2;
 extern struct	excludes *excludes_list;
 extern regex_t	ignore_re;
Index: usr.bin/diff/diff.1
===================================================================
--- usr.bin/diff/diff.1
+++ usr.bin/diff/diff.1
@@ -44,6 +44,7 @@
 .Fl n | q | u | y
 .Oc
 .Op Fl -brief
+.Op Fl -color Ns = Ns Ar when
 .Op Fl -changed-group-format Ar GFMT
 .Op Fl -ed
 .Op Fl -expand-tabs
@@ -71,6 +72,7 @@
 .Op Fl I Ar pattern | Fl -ignore-matching-lines Ar pattern
 .Op Fl L Ar label | Fl -label Ar label
 .Op Fl -brief
+.Op Fl -color Ns = Ns Ar when
 .Op Fl -changed-group-format Ar GFMT
 .Op Fl -ed
 .Op Fl -expand-tabs
@@ -96,6 +98,7 @@
 .Op Fl aBbdiltw
 .Op Fl I Ar pattern | Fl -ignore-matching-lines Ar pattern
 .Op Fl -brief
+.Op Fl -color Ns = Ns Ar when
 .Op Fl -changed-group-format Ar GFMT
 .Op Fl -ed
 .Op Fl -expand-tabs
@@ -122,6 +125,7 @@
 .Op Fl I Ar pattern | Fl -ignore-matching-lines Ar pattern
 .Op Fl L Ar label | Fl -label Ar label
 .Op Fl -brief
+.Op Fl -color Ns = Ns Ar when
 .Op Fl -changed-group-format Ar GFMT
 .Op Fl -ed
 .Op Fl -expand-tabs
@@ -150,6 +154,7 @@
 .Fl n | q | u
 .Oc
 .Op Fl -brief
+.Op Fl -color Ns = Ns Ar when
 .Op Fl -changed-group-format Ar GFMT
 .Op Fl -context
 .Op Fl -ed
@@ -184,6 +189,7 @@
 .Ar dir1 dir2
 .Nm diff
 .Op Fl aBbditwW
+.Op Fl -color Ns = Ns Ar when
 .Op Fl -expand-tabs
 .Op Fl -ignore-all-blanks
 .Op Fl -ignore-blank-lines
@@ -332,6 +338,17 @@
 .It Fl b -ignore-space-change
 Causes trailing blanks (spaces and tabs) to be ignored, and other
 strings of blanks to compare equal.
+.It Fl Fl color= Ns Oo Ar when Oc
+Mark up the matching text with the expression stored in the
+.Ev DIFFCOLOR
+environment variable.
+The possible values of
+.Ar when
+are
+.Dq Cm never ,
+.Dq Cm always
+and
+.Dq Cm auto .
 .It Fl d -minimal
 Try very hard to produce a diff as small as possible.
 This may consume a lot of processing power and memory when processing
Index: usr.bin/diff/diff.c
===================================================================
--- usr.bin/diff/diff.c
+++ usr.bin/diff/diff.c
@@ -38,11 +38,12 @@
 #include "diff.h"
 #include "xmalloc.h"
 
-int	 lflag, Nflag, Pflag, rflag, sflag, Tflag, cflag, Wflag;
+int	 lflag, Nflag, Pflag, rflag, sflag, Tflag, cflag, Wflag, colorflag = 0;
 int	 diff_format, diff_context, status, ignore_file_case, suppress_common;
 int	 tabsize = 8, width = 130;
 char	*start, *ifdefname, *diffargs, *label[2], *ignore_pats;
 char	*group_format = NULL;
+const char	*add_code, *del_code;
 struct stat stb1, stb2;
 struct excludes *excludes_list;
 regex_t	 ignore_re;
@@ -57,6 +58,7 @@
 	OPT_HORIZON_LINES,
 	OPT_CHANGED_GROUP_FORMAT,
 	OPT_SUPPRESS_COMMON,
+	OPT_COLOR,
 };
 
 static struct option longopts[] = {
@@ -97,6 +99,7 @@
 	{ "tabsize",			required_argument,	NULL,	OPT_TSIZE },
 	{ "changed-group-format",	required_argument,	NULL,	OPT_CHANGED_GROUP_FORMAT},
 	{ "suppress-common-lines",	no_argument,		NULL,	OPT_SUPPRESS_COMMON },
+	{ "color",			optional_argument,	NULL,	OPT_COLOR },
 	{ NULL,				0,			0,	'\0'}
 };
 
@@ -106,6 +109,7 @@
 void push_ignore_pats(char *);
 void read_excludes_file(char *file);
 void set_argstr(char **, char **);
+static const char *init_code(int, const char *);
 
 int
 main(int argc, char **argv)
@@ -301,6 +305,21 @@
 		case OPT_SUPPRESS_COMMON:
 			suppress_common = 1;
 			break;
+		case OPT_COLOR:
+			if (optarg == NULL || strncmp(optarg, "auto", 4) == 0)
+				colorflag = isatty(STDOUT_FILENO) ? 1 : 0;
+			else if (strncmp(optarg, "always", 6) == 0)
+				colorflag = 1;
+			else if (strncmp(optarg, "never", 5) == 0)
+				colorflag = 0;
+			else
+				errx(2, "unsupported --color value '%s' (must be always, auto, or never)",
+					optarg);
+			if (colorflag) {
+				add_code = init_code(1, "32");
+				del_code = init_code(2, "31");
+			}
+			break;
 		default:
 			usage();
 			break;
@@ -550,3 +569,21 @@
 	fprintf(stderr, "error: conflicting output format options.\n");
 	usage();
 }
+
+static const char *
+init_code(int i, const char *rv)
+{
+	char *buf, *p, *env;
+	int j;
+
+	env = getenv("DIFFCOLORS");
+	if (env != NULL && *env != '\0') {
+		p = strdup(env);
+		for (j = 0; j < i; j++)
+			buf = strsep(&p, ":");
+		free(p);
+		if (buf != NULL)
+			return buf;
+	}
+	return rv;
+}
Index: usr.bin/diff/diffreg.c
===================================================================
--- usr.bin/diff/diffreg.c
+++ usr.bin/diff/diffreg.c
@@ -1183,13 +1183,23 @@
 		}
 	}
 	if (diff_format == D_SIDEBYSIDE) {
+		if (colorflag && (a>b))
+			printf("\033[%sm", add_code);
+		else if (colorflag && (c>d))
+			printf("\033[%sm", del_code);
 		if (a > b) {
 			print_space(0, hw + padding , *pflags);
 		} else {
 			nc = fetch(ixold, a, b, f1, '\0', 1, *pflags);
 			print_space(nc, hw - nc + padding, *pflags);
 		}
+		if (colorflag && (a>b))
+			printf("\033[%sm", add_code);
+		else if (colorflag && (c>d))
+			printf("\033[%sm", del_code);
 		printf("%c", (a>b)? '>' : ((c>d)? '<' : '|'));
+		if (colorflag && (c>d))
+			printf("\33[m");
 		print_space(hw + padding + 1 , padding, *pflags);
 		fetch(ixnew, c, d, f2, '\0', 0, *pflags);
 		printf("\n");
@@ -1263,6 +1273,10 @@
 			nc = hw;
 		if ((diff_format != D_IFDEF && diff_format != D_GFORMAT) &&
 		    ch != '\0') {
+			if (colorflag && (ch == '>' || ch == '+'))
+				printf("\033[%sm", add_code);
+			else if (colorflag && (ch == '<' || ch == '-'))
+				printf("\033[%sm", del_code);
 			printf("%c", ch);
 			if (Tflag && (diff_format == D_NORMAL ||
 			    diff_format == D_CONTEXT ||
@@ -1335,6 +1349,8 @@
 			}
 		}
 	}
+	if (colorflag)
+		printf("\33[m");
 	return col;
 }