Preserve color() names and use as labels in plot()

[gadenbuie]

This PR does two things:

1. color() now retains the names of the original vector, if present
2. plot.colors() uses the color names when label = TRUE, or label can be provided a character vector of color names.

Together, these changes make it easier to use plot() to show off a named color palette.

Take this completely random color palette as an example.

clrs <- c(
  blue = "#447098FF", orange = "#ED6331FF", gray = "#404041FF", 
  teal = "#419498FF", green  = "#72984EFF", burgundy = "#994665FF"
)

When passed to color(), the original color names are retained.

pkgload::load_all()
#> ℹ Loading prismatic
clrs <- color(clrs)
clrs
#> <colors>
#> #447098FF #ED6331FF #404041FF #419498FF #72984EFF #994665FF
names(clrs)
#> [1] "blue"     "orange"   "gray"     "teal"     "green"    "burgundy"

The default plot methods works as previously (labels = FALSE by default)

plot(clrs)

But if labels are requested and if the input vector is named, the names are used for the color labels.

plot(clrs, labels = TRUE)

If the input vector is unnamed, the HEX value of the color is presented (previous behavior).

plot(unname(clrs), labels = TRUE)

Finally, you can also provide labels a character vector equal in length to x if you'd like to use a different label for each color.

plot(clrs, labels = paste("Posit", stringr::str_to_title(names(clrs))))

[EmilHvitfeldt]

Looking good! Can you add a quick NEWS bullet as well? That would be awesome

[EmilHvitfeldt]

Thank you!