Package color Error: Argument `1.01125' not in range [0,1]

Question

I have been writing a paper and used tikz for some of my figures. Then when we decided to submit to a particular conference, and used the style file they provided, the figure broke (failed to compile). I dissected their style file and found that the line "\p@=1bp" is responsible for the problem, but I do not know what that line is and how to work around it. Simply removing the line is not a solution since I have no control over the style file they will use for the final publishable version.

This version works correctly:

\documentclass{minimal}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
  \fill [blue!25] (1,1) rectangle (2,2);
\end{tikzpicture}
\end{document}

This version generates the error mentioned in the title:

\documentclass{minimal}
\makeatletter
\p@=1bp
\makeatother
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
  \fill [blue!25] (1,1) rectangle (2,2);
\end{tikzpicture}
\end{document}

Curiously, it works again when I remove the "!25" after "blue":

\documentclass{minimal}
\makeatletter
\p@=1bp
\makeatother
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
  \fill [blue] (1,1) rectangle (2,2);
\end{tikzpicture}
\end{document}

I am using pdflatex: pdfTeX 3.14159265-2.6-1.40.17 (TeX Live 2016/MacPorts 2016_4).

I am looking for a way to specify the color "blue!25" without modifying the style file. That is, with the following snippet present in the preamable:

\makeatletter
\p@=1bp
\makeatother

Thank you.

Answer 1

\p@ is originally defined as 1.0pt. After \p@=1bp it has the value 1.00374pt. I suggest to add the lines

\makeatletter
\p@=1pt
\makeatother

to the preamble after loading dgruyter_NEW.sty.

Edit: The issue is still present in the most recent version of de Gruyter's LaTeX package. One of the first lines in dgruyter.sty (identifying itself as 2016/09/28 v1.82 De Gruyter layout) still reads \p@=1bp\relax, which leads to the error described in the original post.

Answer 2

Actually I get no error on the supplied test file however

\makeatletter
\p@=1bp
\makeatother

is spectacularly wrong and will break almost all latex arithmetic, not only color, but the graphics package, arithmetic by the calc package, tabularx, .....

To see why note that latex has no floating point registers, only lengths or integers so if for example you are mixing colours and need to multiply .3 by 2 the usual way is to go via lengths

\dimen@=.3\p@

now \dimen@ is .3pt

\dimen@=2\dimen@

now it is .6pt

\edef\result{\strip@pt\dimen@}
\show\result

removes the pt

> \result=macro:
->0.6.

But now redefine \p@ to be 1bp the same calculation ends up with

> \result=macro:
->0.60223.

so even the simplest arithmetic operation gives an incorrect result.