Add examples of how to use non-default colour palettes (closes #24)

vignettes/colours.Rmd

@@ -163,13 +163,13 @@ Follow the [advice for using the focus palette](https://analysisfunction.civilse
 The [Scottish Government focus palette](#focus-chart-palette) does not have this issue, so you may wish to use this instead.
 
 
-## Using a different colour palette
+## Using your own colour palette
 
 There may be instances where you'd like to use a different colour palette. 
 If so, this should be carefully considered to ensure it meets accessibility requirements. 
 The Analysis Function guidance outlines [appropriate steps for choosing your own accessibile colour palette](https://analysisfunction.civilservice.gov.uk/policy-store/data-visualisation-colours-in-charts/#section-9) and should be used.
 
-An example of how to use an alternative colour palette is provided in the [cookbook](https://datasciencescotland.github.io/sgplot/articles/cookbook.html#using-a-different-colour-palette).
+An example of how to use an alternative colour palette is provided in the [cookbook](https://datasciencescotland.github.io/sgplot/articles/cookbook.html#using-your-own-colour-palette).
 However, if you use a different palette regularly and feel it would be useful for this to be added to sgplot, please make a suggestion as per the [contributing guidance](https://datasciencescotland.github.io/sgplot/CONTRIBTUING.html).
 
 
@@ -191,4 +191,4 @@ sgplot::sg_colour_palettes$main
 sgplot::af_colour_palettes
 ```
 
-The reference files for `scale_` [colour functions](https://datasciencescotland.github.io/sgplot/reference/index.html#colours) provide examples of how to apply these palettes to ggplot2 charts.
+Examples of how to apply these palettes to ggplot2 charts are available in both the [cookbook](https://datasciencescotland.github.io/sgplot/articles/cookbook.html) and the reference files for `scale_` [colour functions](https://datasciencescotland.github.io/sgplot/reference/index.html#colours).

vignettes/cookbook/_colour-palettes.Rmd

@@ -1,15 +1,78 @@
-## Using a different colour palette
+## Using different colour palettes
 
 sgplot provides colour palettes as set out by the [Scottish Government Design System](https://designsystem.gov.scot/guidance/charts/data-visualisation-colour-palettes). 
 These palettes have been developed to meet the [Web Content Accessibility Guidelines 2.1 for graphical objects](https://www.w3.org/WAI/WCAG21/Understanding/non-text-contrast.html).
 
 The Analysis Function guidance also contains [suggested colour palettes](https://analysisfunction.civilservice.gov.uk/policy-store/data-visualisation-colours-in-charts/#section-4). 
 These are also provided in sgplot, however the Scottish Government palettes are used by default. 
-To use an Analysis Function palette, set `palette_type = "af"` when using any of the `scale_` [colour functions](https://datasciencescotland.github.io/sgplot/reference/index.html#colours).
+The [main palette](https://datasciencescotland.github.io/sgplot/articles/colours.html#main-palette) is the default for discrete colour/fill functions, and the [sequential palette](https://datasciencescotland.github.io/sgplot/articles/colours.html#sequential-palette) for continuous colour/fill functions.
 
 More information on the colours used in sgplot can be found at `vignette("colours")`.
 
-There may be instances where you'd like to use a different colour palette. 
+
+### Using non-default sgplot colour palettes
+
+There may be instances where you want to use an sgplot colour palette other than the default. 
+The full list of available palettes can be found by running either `sgplot::sg_colour_palettes` or `sgplot::af_colour_palettes`.
+
+To use the Scottish Government `main-extended` palette:
+
+```{r main-extended, fig.height = 5}
+#| fig.alt = "A multiple line chart using sgplot theme and SG main-extended colour palette."
+
+gapminder |>
+  filter(country %in% c("United Kingdom", "China", "India",
+                        "Sweden", "Namibia", "Brazil")) |>
+  ggplot(aes(x = year, y = lifeExp, colour = country)) +
+  geom_line(linewidth = 1) +
+  theme_sg(legend = "bottom") +
+  scale_colour_discrete_sg("main-extended") +
+  scale_y_continuous(limits = c(0, 82),
+                     breaks = seq(0, 80, 20),
+                     expand = c(0, 0)) +
+  scale_x_continuous(breaks = seq(1952, 2007, 5)) +
+  labs(
+    x = "Year",
+    y = NULL,
+    title = "Living Longer",
+    subtitle = "Life Expectancy in the United Kingdom and China 1952-2007",
+    caption = "Source: Gapminder",
+    colour = NULL
+  )
+```
+
+Note: This chart is for demonstration purposes only. Accessibility guidance recommends using a maximum of four colours to avoid clutter.
+
+To use an Analysis Function palette, set `palette_type = "af"` when using any of the `scale_` [colour functions](https://datasciencescotland.github.io/sgplot/reference/index.html#colours). 
+For example, to use the Analysis Function `main2` palette:
+
+```{r af-palette, fig.height = 5}
+#| fig.alt = "A multiple line chart using sgplot theme and AF main colour palette."
+
+gapminder |>
+  filter(country %in% c("United Kingdom", "China")) |>
+  ggplot(aes(x = year, y = lifeExp, colour = country)) +
+  geom_line(linewidth = 1) +
+  theme_sg(legend = "bottom") +
+  scale_colour_discrete_sg("main2", palette_type = "af") +
+  scale_y_continuous(limits = c(0, 82),
+                     breaks = seq(0, 80, 20),
+                     expand = c(0, 0)) +
+  scale_x_continuous(breaks = seq(1952, 2007, 5)) +
+  labs(
+    x = "Year",
+    y = NULL,
+    title = "Living Longer",
+    subtitle = "Life Expectancy in the United Kingdom and China 1952-2007",
+    caption = "Source: Gapminder",
+    colour = NULL
+  )
+```
+
+
+### Using your own colour palette
+
+There may be instances where you'd like to use a colour palette that is not available in sgplot. 
 If so, this should be carefully considered to ensure it meets accessibility requirements. 
 The Analysis Function guidance outlines [appropriate steps for choosing your own accessibile colour palette](https://analysisfunction.civilservice.gov.uk/policy-store/data-visualisation-colours-in-charts/#section-9) and should be used.
 
@@ -59,6 +122,7 @@ gapminder |>
   )
 ```
 
-### Adding a new colour palette to sgplot
+
+#### Adding a new colour palette to sgplot
 
 If you use a different palette regularly and feel it would be useful for this to be added to sgplot, please make a suggestion as per the [contributing guidance](https://datasciencescotland.github.io/sgplot/CONTRIBTUING.html).