The RGB will show you how much red, green, and blue are needed to create pastel blue as a web color. The hex code is what helps identify colors on the web, along with the RGB and CMYK color codes that help to break down the color composition for each color. Pastel blue, along with all similar shades can be regarded as cool and has the hex code #aec6cf. 6.3 What Is the Meaning of Pastel Blue?.