Similar to @marmots approach, but instead of using only `\draw`, I suggest to also fill the shapes in white. This way also most of the features on the front can be coloured in.

```
\documentclass[varwidth]{standalone}

\usepackage{tikzlings,tikzducks}
\selectcolormodel{gray}

\makeatletter
\def\tikzlinghookbackground{
  \def\bear@part@draw[##1]{\draw[##1,black,fill=white]}
  \def\penguin@part@draw[##1]{\draw[##1,black,fill=white]}
  \def\marmot@part@draw[##1]{\draw[##1,black,fill=white]}
  \def\koala@part@draw[##1]{\draw[##1,black,fill=white]}
  \def\owl@part@draw[##1]{\draw[##1,black,fill=white]}
  \def\coati@part@draw[##1]{\draw[##1,black,fill=white]}
  \def\snowman@part@draw[##1]{\draw[##1,black,fill=white]}
  \def\rhino@part@draw[##1]{\draw[##1,black,fill=white]}
  \def\mole@part@draw[##1]{\draw[##1,black,fill=white]}
  \def\moles@part@draw[##1]{\draw[##1,black,fill=white]}
  \def\sloth@part@draw[##1]{\draw[##1,black,fill=white]}
  \def\pig@part@draw[##1]{\draw[##1,black,fill=white]}
  \def\cat@part@draw[##1]{\draw[##1,black,fill=white]}
  \def\hippo@part@draw[##1]{\draw[##1,black,fill=white]}
  \def\panda@part@draw[##1]{\draw[##1,black,fill=white]}
  \def\sheep@part@draw[##1]{\draw[##1,black,fill=white]}
  \def\squirrel@part@draw[##1]{\draw[##1,black,fill=white]}
  \def\anteater@part@draw[##1]{\draw[##1,black,fill=white]}
  \def\mouse@part@draw[##1]{\draw[##1,black,fill=white]}
  \def\bee@part@draw[##1]{\draw[##1,black,fill=white]} 
}
\makeatother

\begin{document}

\begin{tikzpicture}
\bear[]
\end{tikzpicture}\hfill%
\begin{tikzpicture}
\penguin[]
\end{tikzpicture}\hfill%
\begin{tikzpicture}
\marmot[]
\end{tikzpicture}\hfill%
\begin{tikzpicture}
\koala[]
\end{tikzpicture}\hfill%
\begin{tikzpicture}
\owl[]
\end{tikzpicture}\hfill%
\begin{tikzpicture}
\coati[]
\end{tikzpicture}

\begin{tikzpicture}
\snowman[]
\end{tikzpicture}\hfill%
\begin{tikzpicture}
\rhino[]
\end{tikzpicture}\hfill%
\begin{tikzpicture}
\moles[]
\end{tikzpicture}\hfill%
\begin{tikzpicture}
\sloth[]
\end{tikzpicture}\hfill%
\begin{tikzpicture}
\pig[]
\end{tikzpicture}\hfill%
\begin{tikzpicture}
\cat[]
\end{tikzpicture}

\begin{tikzpicture}
\hippo[]
\end{tikzpicture}\hfill%
\begin{tikzpicture}
\panda[]
\end{tikzpicture}\hfill%
\begin{tikzpicture}
\sheep[]
\end{tikzpicture}\hfill%
\begin{tikzpicture}
\squirrel[]
\end{tikzpicture}\hfill%
\begin{tikzpicture}
\anteater[]
\end{tikzpicture}\hfill%
\begin{tikzpicture}
\mouse[]
\end{tikzpicture}

\begin{tikzpicture}
\bee[]
\end{tikzpicture}%
\end{document}
```

![document.png](/image?hash=d6000b5534f404f2236f9bbffdf6894919f4c88891e0f48da1bceb206996db1e)

(with this approach you can also see where I cheat when drawing, e.g. the nose of the snowman is a combination of two different shapes)

### Edit March 2021

I just added the `contour` option to all tikzlings (https://github.com/samcarter/tikzlings/commit/2f98b504ed50cfa4f154384a8601d59228e71808 , which is included in v0.5 of the TikZlings). You can now use 

```
\marmot[contour]
```

Overview of all TikZlings in contours (front and back):

```
\documentclass[varwidth]{standalone}

\usepackage{tikzlings}

\begin{document}

\makeatletter
\foreach \x/\y in \tikzling@list {
  \begin{tikzpicture}
    \csname\x\endcsname[
      contour=black,
    ]
  \end{tikzpicture}\hfill
}

\foreach \x/\y in \tikzling@list {
  \begin{tikzpicture}
    \csname\x\endcsname[
      back,
      contour=black,
    ]
  \end{tikzpicture}\hfill
}
\makeatother

\end{document}
```

![document.png](/image?hash=e5b6f5e45ff3d6b91b21efe39c6346c65eced50331ef9dd197d6d19c29a24be5)

This is just for fun, I am confident that there is a better way.
```
\documentclass[tikz,border=3mm]{standalone}
\usepackage{tikzlings}
\begin{document}
\begin{tikzpicture}
\begin{scope}[very thick,black]
\let\fill\draw
\marmot[body=black]
\end{scope}
\begin{scope}
\colorlet{black}{white}
\marmot[body=white]
\end{scope}
\end{tikzpicture}
\end{document}
```
![Screen Shot 2020-12-21 at 2.10.44 PM.png](/image?hash=78b205fe14ce3f846a5dd07fdd9fb2f83197d8ddc0d72b589f8fe6e119bca765)