@@ -73,7 +73,7 @@ theme_bw <- function(base_size = 12, base_family = "") {
       axis.text         = element_text(size = rel(0.8)),
       axis.ticks        = element_line(colour = "black"),
       legend.key        = element_rect(colour = "grey80"),
-      panel.background  = element_rect(fill = "white"),
+      panel.background  = element_rect(fill = "white", colour = NA),
       panel.border      = element_rect(fill = NA, colour = "grey50"),
       panel.grid.major  = element_line(colour = "grey90", size = 0.2),
       panel.grid.minor  = element_line(colour = "grey98", size = 0.5),