Change colors without set theme about ggthemr

[Matt-Int]

Hi @Adrian-AlvarezMolina,

I have recreated your issue, and can confirm that using the approach in the README doesn't work.

I also found that using the swatch is the only way to change the colours without changing the theme:

library(ggthemr)

dust_theme <- ggthemr(palette = "dust", set_theme = FALSE)

ggplot(mtcars, aes(mpg, cyl, color = factor(am))) +
    geom_point() +
    dust_theme$theme + 
    scale_color_manual(values = dust_theme$palette$swatch)

As to why the colours do not change, it appears as if the dust_theme$scales does not exist, as per your original comment. I've tracked narrowed it down to this commit from last year, which removed the scales element from the theme structure.

I'll make a pull request to update the readme as this part is no longer accurate.