Color merge from RGB specification

Question

With the xcolor package one can define colors in many ways for example, using standard names,

\colorbox{red}{...}

Merging colors

\colorbox{red!25}{...}

\colorbox{red!25!blue}{...}

Or from the RGB or CYMK values

\colorbox[rgb]{0.1,0.2,0.3}{...}

Is it possible to combine inline the RGB and merging approaches? For example

\colorbox[rgb]{0.1,0.2,0.3 ! 25}{...} %invalid code

\colorbox{\color[rgb]{0.70,0.05,0.65}!25}{...} %also invalid

To make a given RGB color lighter. The context is that for a given element I know the RGB value but I want to make it lighter by merging with white.

MWE:

\documentclass[]{article}
\usepackage[]{xcolor}
\begin{document}
\colorbox[rgb]{0.70,0.05,0.65}{A} % this turns to be dark violet, how to get something like {violet!25}
\end{document}

Answer 1

Sure you can do it. The xcolor package offers a very sofisticated extended syntax for mixing colors (refer to pages 14-16 of the xcolor documentation for details):

\documentclass[]{article}
\usepackage[]{xcolor}
\begin{document}
\colorbox{rgb:red,0.70;green,0.05;blue,0.65}{A} % this turns to be dark violet, how to 

\colorbox{rgb:red!40,0.70;green!40,0.05;blue!40,0.65}{A}

\colorbox{rgb:red!10,0.70;green!10,0.05;blue!10,0.65}{A}
\end{document}

Some more "in-line" shades:

\documentclass{article}
\usepackage[]{xcolor}
\usepackage{pgffor}

\begin{document}
\noindent
\colorbox{rgb:red,0.70;green,0.05;blue,0.65}{A}\quad % this turns to be dark violet, how to 
\foreach \Valor in {90,80,...,10}
{%
  \colorbox{rgb:red!\Valor,0.70;green!\Valor,0.05;blue!\Valor,0.65}{A}\quad
}
\end{document}

In fact, you can produce many variations using this method and, more complexes mixes or, for example, the complement operator -. A little example showing "in-line" variations of your initial color:

\documentclass[]{article}
\usepackage[]{xcolor}
\begin{document}
\colorbox{rgb:red,0.70;green,0.05;blue,0.65}{A} % this turns to be dark violet, how to 

\colorbox{rgb:red!40,0.70;green!40,0.05;blue!40,0.65}{A}

\colorbox{rgb:red!10,0.70;green!10,0.05;blue!10,0.65}{A}

\colorbox{rgb:red!10!cyan,0.70;green!60!cyan,0.05;blue!10,0.65}{A}

\colorbox{rgb:-red!10!cyan,0.70;green!60!cyan,0.05;blue!10,0.65}{A}

\colorbox{rgb:red!10!cyan,0.70;-green!60!cyan,0.05;blue!10!orange,0.65}{A}

\colorbox{rgb:-red!10!cyan,0.70;-green!60!cyan,0.05;blue!10!orange,0.65}{A}
\end{document}

Answer 2

Typically this is done by defining the colour first, after which you can shade (or merge it):

\documentclass{article}
\usepackage{xcolor}
\definecolor{violet}{rgb}{0.70,0.05,0.65}
\begin{document}
\colorbox[rgb]{0.70,0.05,0.65}{A} % this turns to be dark violet, how to get something like {violet!25}

\colorbox{violet}{A}

\colorbox{violet!25}{A}
\end{document}

Answer 3

You could define a wrapper command e.g. \rgbbox[<optional proportion>]{<rgb specification>}{<contents>}. For example:

\documentclass{article}
\usepackage{xcolor}
\newcommand\rgbbox[3][100]{%
  \definecolor{rgbboxcolour}{rgb}{#2}%
  \colorbox{rgbboxcolour!#1}{#3}%
}
\begin{document}
\colorbox[rgb]{0.70,0.05,0.65}{A} % this turns to be dark violet, how to get something like {violet!25}

\rgbbox[25]{0.70,0.05,0.65}{B}

\rgbbox[50]{.25,.75,.75}{C}

\rgbbox{.25,.75,.75}{D}
\end{document}

Note that if the optional argument is not specified, you get no mixing i.e. 100% of the colour given in the first mandatory argument.