diff --git a/.lintr b/.lintr
index def1262..3706d7d 100644
--- a/.lintr
+++ b/.lintr
@@ -1,5 +1,6 @@
 linters: linters_with_defaults(
-    pipe_consistency_linter(pipe = "auto")
+    pipe_consistency_linter(pipe = "auto"),
+    object_name_linter(styles = "snake_case", regexes = c("na\\.value"))
   )
 exclude: "^#| fig.alt = "
 encoding: "UTF-8"
diff --git a/NEWS.md b/NEWS.md
index 08a201d..5a2f8d4 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -1,5 +1,9 @@
 # sgplot (development version)
 
+* Deprecate `na_colour` arguments in `scale_fill_continuous_sg()`/
+`scale_colour_continuous_sg()` functions in favour of new argument, `na.value` 
+(#73).
+
 * Vignettes are converted to articles. Vignettes are now not available to view 
 locally and only via the 
 [pkgdown site](https://scotgovanalysis.github.io/sgplot/) (#66).
diff --git a/R/scale_continuous_sg.R b/R/scale_continuous_sg.R
index 59a3fb2..b76cb8d 100644
--- a/R/scale_continuous_sg.R
+++ b/R/scale_continuous_sg.R
@@ -2,9 +2,10 @@
 #'
 #' @param palette Name of palette to use; e.g. "main", "sequential", "focus".
 #' Default value is "sequential".
-#' @param na_colour Colour to set for missing values.
+#' @param na.value Colour to set for missing values.
 #' @param guide A name or function used to create guide. Default is "colourbar".
 #' @inheritParams scale_colour_discrete_sg
+#' @param na_colour `r lifecycle::badge('deprecated')` Use `na.value` instead.
 #'
 #' @returns ggplot2 continuous colour/fill scale
 #'
@@ -24,9 +25,19 @@
 scale_colour_continuous_sg <- function(palette = "sequential",
                                        palette_type = "sg",
                                        reverse = FALSE,
-                                       na_colour = "grey50",
+                                       na.value = "grey50",
                                        guide = "colourbar",
-                                       ...) {
+                                       ...,
+                                       na_colour = deprecated()) {
+
+  if (lifecycle::is_present(na_colour)) {
+    lifecycle::deprecate_warn(
+      when = "0.4.0",
+      what = "scale_colour_continuous_sg(na_colour)",
+      with = "scale_colour_continuous_sg(na.value)"
+    )
+    na.value <- na_colour
+  }
 
   colours <-
     sg_palette(palette = palette,
@@ -36,7 +47,7 @@ scale_colour_continuous_sg <- function(palette = "sequential",
   ggplot2::continuous_scale(
     aesthetics = "colour",
     palette    = scales::gradient_n_pal(colours, values = NULL, "Lab"),
-    na.value   = na_colour,
+    na.value   = na.value,
     guide      = guide,
     ...
   )
@@ -49,9 +60,19 @@ scale_colour_continuous_sg <- function(palette = "sequential",
 scale_fill_continuous_sg <- function(palette = "sequential",
                                      palette_type = "sg",
                                      reverse = FALSE,
-                                     na_colour = "grey50",
+                                     na.value = "grey50",
                                      guide = "colourbar",
-                                     ...) {
+                                     ...,
+                                     na_colour = deprecated()) {
+
+  if (lifecycle::is_present(na_colour)) {
+    lifecycle::deprecate_warn(
+      when = "0.4.0",
+      what = "scale_fill_continuous_sg(na_colour)",
+      with = "scale_fill_continuous_sg(na.value)"
+    )
+    na.value <- na_colour
+  }
 
   colours <-
     sg_palette(palette = palette,
@@ -61,7 +82,7 @@ scale_fill_continuous_sg <- function(palette = "sequential",
   ggplot2::continuous_scale(
     aesthetics = "fill",
     palette    = scales::gradient_n_pal(colours, values = NULL, "Lab"),
-    na.value   = na_colour,
+    na.value   = na.value,
     guide      = guide,
     ...
   )
diff --git a/R/use_sgplot.R b/R/use_sgplot.R
index d9f6bb4..cdd1da3 100644
--- a/R/use_sgplot.R
+++ b/R/use_sgplot.R
@@ -67,17 +67,17 @@ use_sgplot <- function(palette_type = "sg",
   # Use sgplot colour palette ----
 
   options(
-    ggplot2.continuous.fill = function() {
-      scale_fill_continuous_sg(palette_type = palette_type)
+    ggplot2.continuous.fill = function(...) {
+      scale_fill_continuous_sg(palette_type = palette_type, ...)
     },
-    ggplot2.continuous.colour = function() {
-      scale_colour_continuous_sg(palette_type = palette_type)
+    ggplot2.continuous.colour = function(...) {
+      scale_colour_continuous_sg(palette_type = palette_type, ...)
     },
-    ggplot2.discrete.fill = function() {
-      scale_fill_discrete_sg(palette_type = palette_type)
+    ggplot2.discrete.fill = function(...) {
+      scale_fill_discrete_sg(palette_type = palette_type, ...)
     },
-    ggplot2.discrete.colour = function() {
-      scale_colour_discrete_sg(palette_type = palette_type)
+    ggplot2.discrete.colour = function(...) {
+      scale_colour_discrete_sg(palette_type = palette_type, ...)
     }
   )
 
diff --git a/man/scale_colour_continuous_sg.Rd b/man/scale_colour_continuous_sg.Rd
index f1d0a34..f2a5cb3 100644
--- a/man/scale_colour_continuous_sg.Rd
+++ b/man/scale_colour_continuous_sg.Rd
@@ -9,18 +9,20 @@ scale_colour_continuous_sg(
   palette = "sequential",
   palette_type = "sg",
   reverse = FALSE,
-  na_colour = "grey50",
+  na.value = "grey50",
   guide = "colourbar",
-  ...
+  ...,
+  na_colour = deprecated()
 )
 
 scale_fill_continuous_sg(
   palette = "sequential",
   palette_type = "sg",
   reverse = FALSE,
-  na_colour = "grey50",
+  na.value = "grey50",
   guide = "colourbar",
-  ...
+  ...,
+  na_colour = deprecated()
 )
 }
 \arguments{
@@ -33,11 +35,13 @@ available palette types, run \code{available_palette_types()}.}
 \item{reverse}{Boolean value to indicate whether the palette should be
 reversed.}
 
-\item{na_colour}{Colour to set for missing values.}
+\item{na.value}{Colour to set for missing values.}
 
 \item{guide}{A name or function used to create guide. Default is "colourbar".}
 
 \item{...}{Additional arguments passed to scale type.}
+
+\item{na_colour}{\ifelse{html}{\href{https://lifecycle.r-lib.org/articles/stages.html#deprecated}{\figure{lifecycle-deprecated.svg}{options: alt='[Deprecated]'}}}{\strong{[Deprecated]}} Use \code{na.value} instead.}
 }
 \value{
 ggplot2 continuous colour/fill scale