[Tex/LaTex] Why does \color{blue} differ from \color{Blue}

Question

    \documentclass[dvipsnames]{article}
    \usepackage{xcolor}
    \begin{document}
    {\color{Blue}\bf Blue} versus {\color{blue}\bf blue}.
    \end{document}

Why does one of them differ from the other one?

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EDIT 1

1. I still wonder why the color is distinguished by capitalization 🙂
2. Why did the package author choose dvipsnames as the option name? I think this name potentially makes us obtain a wrong impression from it that is usually used to describe the driver? In fact both pdflatex and latex can use it, right?

Answer 1

A natural color is defined by its wavelength. If you want to print it you have to convert it into a color model which allows the mixing of base colors into the needed color. Such color models are very different and a blue in model A is often different to a blue in model B.

"blue" is a rgb color and "Blue" is defined as a cmyk color and handled by a different driver for your output. If you want to be sure, that you use the same driver, then specify one:

\documentclass[dvipsnames]{article}


\usepackage[rgb]{xcolor}

\begin{document}

{\color{Blue}\bf Blue} versus {\color{blue}\bf blue}.

\end{document}

instead of [rgb] you can also use [cmyk]