Colouring theorem environment

Question

I would like to change the theorem environment so that the title and name are coloured. What can I do? Have checked ways to do this (e.g. with \newtheoremstyle) but have not worked well yet. I do not want to use theorom packages such as amsthm, but stick with basic built-in theorem structure.

\documentclass[12pt]{article}
\usepackage[b5paper,body={13cm,18cm}]{geometry}
\usepackage{xcolor}
\begin{document}
\begin{theorem}[Continuous Function]
  Let (f) be a function whose derivative exists in every point,
  then (f) is a continuous function.
\end{theorem}
\end{document}

I would have other environments using \newtheorem that I would want the same colouring scheme as would happen with \begin{theorem} ... \end{theorem}.

Can you add a minimal working example so we can see which of the theorem packages you are using? — samcarter_is_at_topanswers.xyz, Sep 07 '22 at 10:48
Does this answer your question? Changing the color of theorem headings — campa, Sep 07 '22 at 11:18
That example does not even compile. You still need to define theorem. This should be diable using thmtools (haven't tested it) or directly via amsthm and defining custom theorem styles. — daleif, Sep 07 '22 at 11:49
I want to use the built-in latex functionality to do it without amsthm. Doable but how? — Veak, Sep 07 '22 at 13:07
If you ask someone a direct question please use @name to notify. thmtools works with regular \newtheorem. What is wrong with using amsthm? You're already using xcolor so what is the point is requiring build-in latex functionality? — daleif, Sep 07 '22 at 13:26
I'm voting to leave open because the OP asks for a solution without amsthm, which makes it a different question. — Marijn, Sep 07 '22 at 13:27
@konmi -- If you don't want to use amsthm or other particular packages, please add that to your question. — barbara beeton, Sep 07 '22 at 15:42
There isn't any such thing as "basic builtin theorem structure" as far as I know. Your current code does not compile because no theorem environment is defined. Why don't you want to use amsthm? How are you defining theorem environments now? — frabjous, Sep 07 '22 at 16:59
@frabjous do remember that \newtheorem is in the core. The op does not need amsthm, it is just a strange requirement to not use packages — daleif, Sep 07 '22 at 18:20
Here is where we disagree. I only want to change colour for something that is in core without relying on theorem packages. — Veak, Sep 07 '22 at 19:03

score 1 · Answer 1 · answered Feb 04 '23 at 23:38

In https://tex.stackexchange.com/a/17555/4427 you find the default values for theorem styles. You just need to tailor the last argument to your needs.

\documentclass{article}
\usepackage{amsthm}
\usepackage{xcolor}
\newtheoremstyle{colorplain}
  {\topsep}   % ABOVESPACE
  {\topsep}   % BELOWSPACE
  {\itshape}  % BODYFONT
  {0pt}       % INDENT (empty value is the same as 0pt)
  {\bfseries} % HEADFONT
  {.}         % HEADPUNCT
  {5pt plus 1pt minus 1pt} % HEADSPACE
  {%
   \thmnumber{\textcolor{red!75}{#1}}%
   \ % space
   \thmname{\textcolor{green!60!red}{#2}}%
   \thmnote{ \textcolor{blue!80!green}{#3}}%
  }
\theoremstyle{colorplain}
\newtheorem{theorem}{Theorem}
\begin{document}
\begin{theorem}
This has no theorem note.
\end{theorem}
\begin{theorem}[Note]
This has a theorem note.
\end{theorem}
\end{document}

But this is definitely ugly. I believe you just want one color for the whole heading.

\documentclass{article}
\usepackage{amsthm}
\usepackage{xcolor}
\newtheoremstyle{colorplain}
  {\topsep}   % ABOVESPACE
  {\topsep}   % BELOWSPACE
  {\itshape}  % BODYFONT
  {0pt}       % INDENT (empty value is the same as 0pt)
  {\color{blue!80!green}\bfseries} % HEADFONT
  {.}         % HEADPUNCT
  {5pt plus 1pt minus 1pt} % HEADSPACE
  {}
\theoremstyle{colorplain}
\newtheorem{theorem}{Theorem}
\begin{document}
\begin{theorem}
This has no theorem note.
\end{theorem}
\begin{theorem}[Note]
This has a theorem note.
\end{theorem}
\end{document}

murray · Answer 2 · 2022-09-07T18:44:36.543

Albeit using both the amsthm and thmtools environments, something like this?

(I also corrected the run-on sentence and corrected the preposition "in" to be "at.")

\documentclass[12pt]{article}
\usepackage[b5paper,body={13cm,18cm}]{geometry}
\usepackage{xcolor}  
\usepackage{amsmath,amsthm}
\usepackage{thmtools}
\declaretheoremstyle[
  headfont={\color{red}\bfseries},
  notefont={\color{blue}},
]{thmstyle}
%
\declaretheorem[name=Theorem, style=thmstyle]{theorem}
\begin{document}
\begin{theorem}[Continuous Function]
  If (f) is a function whose derivative exists at every point,
  then (f) is a continuous function.
\end{theorem}
\end{document}

Colouring theorem environment

2 Answers2