Here, we will want to make the blue color transparent so we can fill it in ourselves. Using a Chrome eye dropper plugin, I found the color we need to make transparent is: #3183bf. We can set this to transparent using the image_transparent() function from the magick package, then use as.raster() to make it something R can plot again. Source: almost 3 years ago

In this case they can use a browser extension like Eye Dropper to give you an accurate answer. Source: about 3 years ago

Depends on the environment/framework you would use. Eg. I use https://casesandberg.github.io/react-color/ as color selector for react. Source: almost 3 years ago