r color: how to get color values from a scale_color_continuous

Question

For example, there is a numeric variable array like (1.3,4.5,5.4,3.7,2.8....). When we use ggplot and scale_color_continuous, we can get a color bar for it. How can I get the values of this bar so that I can use the same color values to somewhere else? I mean, I want to put these color values to a data.frame as a column. Any help will be appreciated.