Set grid colour in panel.grid

Fixes #2352

NEWS.md

@@ -224,6 +224,10 @@ up correct aspect ratio, and draws a graticule.
 * Complete themes now always override all elements of the default theme
   (@has2k1, #2058, #2079)
 
+* Themes now set default grid colour in `panel.grid` rather than individually
+  in `panel.grid.major` and `panel.grid.minor` individually. This makes it 
+  slightly easier to customise the grid (#2352).
+
 * Fixed bug when setting strips to `element_blank()` (@thomasp85). 
 
 * Axes positioned on the top and to the right can now customize their ticks and

R/theme-defaults.r

@@ -141,8 +141,8 @@ theme_grey <- function(base_size = 11, base_family = "",
 
     panel.background =   element_rect(fill = "grey92", colour = NA),
     panel.border =       element_blank(),
-    panel.grid.major =   element_line(colour = "white"),
-    panel.grid.minor =   element_line(colour = "white", size = rel(0.5)),
+    panel.grid =         element_line(colour = "white"),
+    panel.grid.minor =   element_line(size = rel(0.5)),
     panel.spacing =      unit(half_line, "pt"),
     panel.spacing.x =    NULL,
     panel.spacing.y =    NULL,
@@ -204,8 +204,8 @@ theme_bw <- function(base_size = 11, base_family = "",
       panel.background = element_rect(fill = "white", colour = NA),
       panel.border     = element_rect(fill = NA, colour = "grey20"),
       # make gridlines dark, same contrast with white as in theme_grey
-      panel.grid.major = element_line(colour = "grey92"),
-      panel.grid.minor = element_line(colour = "grey92", size = rel(0.5)),
+      panel.grid = element_line(colour = "grey92"),
+      panel.grid.minor = element_line(size = rel(0.5)),
       # contour strips to match panel contour
       strip.background = element_rect(fill = "grey85", colour = "grey20"),
       # match legend key to background
@@ -239,8 +239,9 @@ theme_linedraw <- function(base_size = 11, base_family = "",
 
       # pure black panel border and grid lines, but thinner
       panel.border     = element_rect(fill = NA, colour = "black", size = rel(1)),
-      panel.grid.major = element_line(colour = "black", size = rel(0.1)),
-      panel.grid.minor = element_line(colour = "black", size = rel(0.05)),
+      panel.grid       = element_line(colour = "black"),
+      panel.grid.major = element_line(size = rel(0.1)),
+      panel.grid.minor = element_line(size = rel(0.05)),
 
       # strips with black background and white text
       strip.background = element_rect(fill = "black"),
@@ -274,8 +275,9 @@ theme_light <- function(base_size = 11, base_family = "",
       panel.border     = element_rect(fill = NA, colour = "grey70", size = rel(1)),
       # light grey, thinner gridlines
       # => make them slightly darker to keep acceptable contrast
-      panel.grid.major = element_line(colour = "grey87", size = rel(0.5)),
-      panel.grid.minor = element_line(colour = "grey87", size = rel(0.25)),
+      panel.grid       = element_line(colour = "grey87"),
+      panel.grid.major = element_line(size = rel(0.5)),
+      panel.grid.minor = element_line(size = rel(0.25)),
 
       # match axes ticks thickness to gridlines and colour to panel border
       axis.ticks       = element_line(colour = "grey70", size = rel(0.5)),
@@ -315,8 +317,9 @@ theme_dark <- function(base_size = 11, base_family = "",
       panel.background = element_rect(fill = "grey50", colour = NA),
       # inverse grid lines contrast compared to theme_grey
       # make them thinner and try to keep the same visual contrast as in theme_light
-      panel.grid.major = element_line(colour = "grey42", size = rel(0.5)),
-      panel.grid.minor = element_line(colour = "grey42", size = rel(0.25)),
+      panel.grid       = element_line(colour = "grey42"),
+      panel.grid.major = element_line(size = rel(0.5)),
+      panel.grid.minor = element_line(size = rel(0.25)),
 
       # match axes ticks thickness to gridlines
       axis.ticks       = element_line(colour = "grey20", size = rel(0.5)),