Use \macro within xcolor expression

Question

So this seems to be impossible:

OrangeRed!\c!white

with \c being any kind of \def formula, or precisely in my case, with a \pgfmathsetmacro. Here is MWE

\documentclass{article}

\usepackage{mathtools}

% TIKZ & PGF
\usepackage[usenames,dvipsnames,svgnames]{xcolor}
\usepackage{pgfplots}
\pgfplotsset{compat=newest}
\usepackage{tikz}

\usetikzlibrary{backgrounds, decorations.shapes, decorations.markings, shapes, patterns}

% % % % % % % % CIRCLES % % % % % % % %
% #1 angle
% #2 ray
% #3 shift
\pgfmathdeclarefunction{circleX}{3}
{%
    \pgfmathparse{#3 + #2*cos(deg(#1))}%
}
\pgfmathdeclarefunction{circleY}{3}
{%
    \pgfmathparse{#3 + #2*sin(deg(#1))}%
}

\begin{document}
    \begin{tikzpicture}


        \tikzset{
            small dot/.style={fill=black, circle, scale=2}
        }

        \pgfmathsetmacro{\halfPi}{.5*pi}
        \pgfmathsetmacro{\twoPi}{2*pi}

        \pgfmathsetmacro{\r}{1}
        \pgfmathsetmacro{\yshift}{0.25}

        \begin{axis}[axis x line=center, axis y line=none, width=.5\textwidth, axis equal,
                     xtick={0,\halfPi,...,\twoPi}, xticklabels={$0$,$\frac{\pi}{2}$,$\pi$,$\frac{3\pi}{2}$,$2\pi$}]


            \foreach \i in {0.25,0.5,...,1} { %
                \pgfmathsetmacro{\c}{(1.2-\i)*100}
                \pgfmathsetmacro{\xshift}{\i*2*pi}

                %\addplot[OrangeRed!\c!white -> nope
                %\addplot[color=OrangeRed!\c!white -> nope
                %\addplot[color={OrangeRed!\c!white} -> nope
                %\addplot[color/.expanded=OrangeRed!\c!white -> nope

                \addplot[color=OrangeRed!50!white, samples=80, domain=0:2*pi]
                    ({circleX(x,\r,\xshift)},{circleY(x,\r,\r+\yshift)});
            }

        \end{axis}
    \end{tikzpicture}
\end{document}

Is there any way to use a macro within an xcolor expression without the need of a \definecolor{colorname}{rgb|cmyk|...}{color stuff definition}?

Answer 1

You have to expand \c (but I'd use a different name) before \addplot sees it:

\documentclass{article}

% TIKZ & PGF
\usepackage[usenames,dvipsnames,svgnames]{xcolor}
\usepackage{pgfplots}
\pgfplotsset{compat=newest}
\usepackage{tikz}

\usetikzlibrary{backgrounds, decorations.shapes, decorations.markings, shapes, patterns}

% % % % % % % % CIRCLES % % % % % % % %
% #1 angle
% #2 ray
% #3 shift
\pgfmathdeclarefunction{circleX}{3}
 {%
  \pgfmathparse{#3 + #2*cos(deg(#1))}%
 }
\pgfmathdeclarefunction{circleY}{3}
 {%
  \pgfmathparse{#3 + #2*sin(deg(#1))}%
 }

\begin{document}
\begin{tikzpicture}
\tikzset{small dot/.style={fill=black, circle, scale=2}}
\pgfmathsetmacro{\halfPi}{.5*pi}
\pgfmathsetmacro{\twoPi}{2*pi}
\pgfmathsetmacro{\r}{1}
\pgfmathsetmacro{\yshift}{0.25}
\begin{axis}[
  axis x line=center,
  axis y line=none,
  width=.5\textwidth,
  axis equal,
  xtick={0,\halfPi,...,\twoPi},
  xticklabels={$0$,$\frac{\pi}{2}$,$\pi$,$\frac{3\pi}{2}$,$2\pi$}
]
\foreach \i in {0.25,0.5,...,1} {%
  \pgfmathsetmacro{\mycol}{(1.2-\i)*100}
  \edef\mycol{OrangeRed!\mycol}
  \pgfmathsetmacro{\xshift}{\i*2*pi}
  \expandafter\addplot\expandafter[%
    \mycol!white,
    samples=80,
    domain=0:2*pi
  ]({circleX(x,\r,\xshift)},{circleY(x,\r,\r+\yshift)});
}
\end{axis}
\end{tikzpicture}
\end{document}

Answer 2

This is the best I've found but I don't know if you'll find it easy enough. It's more or less the same effort required to define a color.

\documentclass{article}
\usepackage{tikz,pgfplots}
\begin{document}
\begin{tikzpicture}
\begin{axis}
\pgfmathsetmacro{\a}{1}
\pgfmathsetmacro{\yshift}{1}
\foreach \i in {0.25,0.5,...,1} {%
  \pgfmathsetmacro{\c}{(1.2-\i)*100}
  \pgfmathsetmacro{\cx}{\i*2*pi}
  \xdef\doplot{\noexpand\addplot[color=red!\c!yellow, samples=80]}
  \doplot ({\cx + \a*cos(deg(x))},{\a + \yshift + \a*sin(deg(x))});
}
\end{axis}
\end{tikzpicture}
\end{document}

---

EDIT: This answered the original question.

This works OK, unless I'm missing something:

\documentclass{article}
\usepackage{xcolor}
\begin{document}
\def\c{50}
Text in a {\color{red!\c!yellow} fancy} color.
\end{document}

Answer 3

It is known that PGFPlots and \foreachs don’t go so nicely together because PGFPlots doesn’t process the plots firstly and then later draws them. (See PGFplots foreach equivalent to TikZ's with multiple variables separated by a slash for more information and explanations of the author of PGFPlot himself.) The package provides the macros

\pgfplotsinvokeforeach{<list>}{<body>}

and

\pgfplotsforeachungrouped <list of variables> in {<list>}{<body>}

The manual even explains the problems and the usage of \edef\temp to “pre-expand” macros.

In your example however, we can avoid this if we postpone the calculation of the color until it is actually plotted/drawn by moving the calculation inside the plot (the \xshift macro is properly expanded in all cases since PGFPlots expects there to be things that needs to be expanded):

\pgfplotsinvokeforeach{0.25,0.5,...,1}{%
  \pgfmathsetmacro{\xshift}{#1*2*pi}
  \addplot[
    /utils/exec=\pgfmathsetmacro\col{(1.2-#1)*100},
    color=OrangeRed!\col!white, samples=80, domain=0:2*pi]
      ({circleX(x,\r,\xshift)},{circleY(x,\r,\r+\yshift)});
}

With my qrr.misc library and its .pgfmath strcat handler you can even do

color/.pgfmath strcat={"OrangeRed!",(1.2-#1)*100,"!white"}

The forest package provides similar handlers (.wrap pgfmath arg), though they fail here, too.