Sharp corners to tcolorbox
You are missing the closing brace in colback=red!15{th} after 15. For me sharp corners works though. I am using version 3.12 (2014/07/29).
As an alternative you can add arc=0pt,outer arc=0pt as the options to tcolorbox to make sharp corners.
\documentclass{article}
\usepackage{tcolorbox}
\tcbuselibrary{theorems}
\tcbuselibrary{skins}
\newtcbtheorem[number within=section]{coloredtheorem}{Theorem}{colback=red!15,arc=0pt,outer arc=0pt}{th}
\begin{document}
\begin{coloredtheorem}{Pigs}{pig}
Pigs are pink.
\end{coloredtheorem}
\end{document}
My solution. Using arc=0pt,outer arc=0pt For The LaTeX package tcolorbox - version 3.04 (2014/05/18).
Documentation of Version 4.11 2017-09-14
/tcb/sharp corners=<position> (default all, initially unset)
The <position> denotes one or more of the four box corners to be set as sharp corners. The not assigned corners will retain their mode.
The /tcb/rounded corners can be used to revert a /tcb/sharp corners setting.
/tcb/sharpish corners (style, no value)
Shortcut for setting /tcb/arc and /tcb/outer arc to 0pt. With this setting, rounded corners will appear as quasi-sharp, but e. g. the shadow will be somewhat rounder than the shadow of really sharp corners.
