Options in newtcolorbox not working

Question

I would like to create a template for my tcolorboxes in my thesis, but I dont seem to get the options to work properly. Here my MWE (the first tcolorbox is the one not using the \newtcolorbox command, just showing the result i want to achieve, and the second is using the \newtcolorbox:

\documentclass[openany,11pt]{book}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{tcolorbox} 

\definecolor{Carmine}{HTML}{960018}%define a color  for code blocks [background Latex Code]


\newtcolorbox{mybox2}[3][Heading]
{
title= \textbf{#1},
colback=#2!5!white, %background color box
colframe=red!50!black, %framecolor box
colbacktitle=#3!85!white, %backgroundcolor titile box
coltitle=white, %color title
%sharp corners,
arc=.3mm, 
fonttitle=\bfseries,
}

\begin{document}

\begin{tcolorbox}[%
colback=red!5!white, %background color box
colframe=red!50!black, %framecolor box
colbacktitle=Carmine!85!white, %backgroundcolor titile box
coltitle=white, %color title
%sharp corners,
arc=.3mm, 
fonttitle=\bfseries,
title= \textbf{Gaspreisfunktion},
]
Zusammensetzung einer \textbf{Indexformel}.
\end{tcolorbox}

\vspace{2cm}


\begin{mybox2}{Uberschrift}{red}{Carmin}
Zusammensetzung einer \textbf{Indexformel}
\end{mybox2}


\end{document}

Answer 1

\newtcolorbox{foo}[3][Heading} defines a tcolorbox with one optional argument (the first one!), to be used with [...] and two mandatory arguments with {} pairs.

The usage

\begin{mybox2}{Uberschrift}{red}{Carmin} is wrong then, it must be \begin{mybox2}[Uberschrift]{red}{Carmine}, also correcting the typo for Carmine.

\documentclass[openany,11pt]{book}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{tcolorbox} 

\definecolor{Carmine}{HTML}{960018}%define a color  for code blocks [background Latex Code]


\newtcolorbox{mybox2}[3][Heading]{
  title= \textbf{#1},
  colback=#2!5!white, %background color box
  colframe=red!50!black, %framecolor box
  colbacktitle=#3!85!white, %backgroundcolor titile box
  coltitle=white, %color title
  % sharp corners,
  arc=.3mm, 
  fonttitle=\bfseries,
}

\begin{document}

\begin{tcolorbox}[%
  colback=red!5!white, %background color box
  colframe=red!50!black, %framecolor box
  colbacktitle=Carmine!85!white, %backgroundcolor titile box
  coltitle=white, %color title
  % sharp corners,
  arc=.3mm, 
  fonttitle=\bfseries,
  title= \textbf{Gaspreisfunktion},
  ]
  Zusammensetzung einer \textbf{Indexformel}.
\end{tcolorbox}

\vspace{2cm}


\begin{mybox2}[Uberschrift]{red}{Carmine}
Zusammensetzung einer \textbf{Indexformel}
\end{mybox2}


\end{document}