URL: http://dwm.suckless.org/patches/historical/float_border_color
float_border_color2 allows you to specify a different border color for floating
windows.

Index: dwm/config.def.h
===================================================================
--- dwm/config.def.h.orig
+++ dwm/config.def.h
@@ -12,10 +12,10 @@ static const char col_gray2[]       = "#
 static const char col_gray3[]       = "#bbbbbb";
 static const char col_gray4[]       = "#eeeeee";
 static const char col_cyan[]        = "#005577";
-static const char *colors[SchemeLast][3]      = {
-	/*               fg         bg         border   */
-	[SchemeNorm] = { col_gray3, col_gray1, col_gray2 },
-	[SchemeSel] =  { col_gray4, col_cyan,  col_cyan  },
+static const char *colors[SchemeLast][4]      = {
+	/*               fg         bg         border     float */
+	[SchemeNorm] = { col_gray3, col_gray1, col_gray2, col_gray2 },
+	[SchemeSel] =  { col_gray4, col_cyan,  col_gray2, col_cyan },
 };
 
 /* tagging */
Index: dwm/dwm.c
===================================================================
--- dwm/dwm.c.orig
+++ dwm/dwm.c
@@ -57,6 +57,7 @@
 #define TAGMASK                 ((1 << LENGTH(tags)) - 1)
 #define TEXTW(X)                (drw_fontset_getwidth(drw, (X)) + lrpad)
 #define ColBorder               2
+#define ColFloat                3
 
 /* enums */
 enum { CurNormal, CurResize, CurMove, CurLast }; /* cursor */
@@ -809,7 +810,10 @@ focus(Client *c)
 		detachstack(c);
 		attachstack(c);
 		grabbuttons(c, 1);
-		XSetWindowBorder(dpy, c->win, scheme[SchemeSel][ColBorder].pixel);
+		if(c->isfloating)
+			XSetWindowBorder(dpy, c->win, scheme[SchemeSel][ColFloat].pixel);
+		else
+			XSetWindowBorder(dpy, c->win, scheme[SchemeSel][ColBorder].pixel);
 		setfocus(c);
 	} else {
 		XSetInputFocus(dpy, root, RevertToPointerRoot, CurrentTime);
@@ -1068,7 +1072,10 @@ manage(Window w, XWindowAttributes *wa)
 
 	wc.border_width = c->bw;
 	XConfigureWindow(dpy, w, CWBorderWidth, &wc);
-	XSetWindowBorder(dpy, w, scheme[SchemeNorm][ColBorder].pixel);
+	if(c->isfloating)
+		XSetWindowBorder(dpy, w, scheme[SchemeNorm][ColFloat].pixel);
+	else
+		XSetWindowBorder(dpy, w, scheme[SchemeNorm][ColBorder].pixel);
 	configure(c); /* propagates border_width, if size doesn't change */
 	updatewindowtype(c);
 	updatesizehints(c);
@@ -1079,6 +1086,8 @@ manage(Window w, XWindowAttributes *wa)
 		c->isfloating = c->oldstate = trans != None || c->isfixed;
 	if (c->isfloating)
 		XRaiseWindow(dpy, c->win);
+	if(c->isfloating)
+		XSetWindowBorder(dpy, w, scheme[SchemeNorm][ColFloat].pixel);
 	attach(c);
 	attachstack(c);
 	XChangeProperty(dpy, root, netatom[NetClientList], XA_WINDOW, 32, PropModeAppend,
@@ -1583,8 +1592,8 @@ setup(void)
 	cursor[CurResize] = drw_cur_create(drw, XC_sizing);
 	cursor[CurMove] = drw_cur_create(drw, XC_fleur);
 	/* init appearance */
-	scheme[SchemeNorm] = drw_scm_create(drw, colors[SchemeNorm], 3);
-	scheme[SchemeSel] = drw_scm_create(drw, colors[SchemeSel], 3);
+	scheme[SchemeNorm] = drw_scm_create(drw, colors[SchemeNorm], 4);
+	scheme[SchemeSel] = drw_scm_create(drw, colors[SchemeSel], 4);
 	/* init bars */
 	updatebars();
 	updatestatus();
@@ -1706,6 +1715,10 @@ togglefloating(const Arg *arg)
 		return;
 	selmon->sel->isfloating = !selmon->sel->isfloating || selmon->sel->isfixed;
 	if (selmon->sel->isfloating)
+		XSetWindowBorder(dpy, selmon->sel->win, scheme[SchemeSel][ColFloat].pixel);
+	else
+		XSetWindowBorder(dpy, selmon->sel->win, scheme[SchemeSel][ColBorder].pixel);
+	if(selmon->sel->isfloating)
 		resize(selmon->sel, selmon->sel->x, selmon->sel->y,
 		       selmon->sel->w, selmon->sel->h, 0);
 	arrange(selmon);