I have been using ggplot2 for 7 years I think. In all that time, I’ve been frustrated that I can never figure out what order to put my color values in for scale_*_manual. Not only is the order mapping seemingly random to me, I know that sometimes if I change something about how I’m treating the data, the order switches up.

Countless hours could have been saved if I knew that this one, in hindsight, obvious thing was possible.

Whenever using scale_*_manual, you can directly reference a color using a character vector and then name your value in the scale_ call like so:

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geom_blah(aes(color = 'good')) +
geom_blah(aes(color = 'bad')) +
scale_blah_manual(values = c(good = 'green', bad = 'red'))

Obviously this is a toy example, but holy game changer.