[AUCTeX] coloring LaTeX code

[Erich Subscriptions]

I see surprising effects when using AucTeX 11.87 on OSX 10.9 with Emacs 24.3

With the following code segment

\newtheorem{thm}{Theorem}
\theoremstyle{definition}
\newtheorem{defn}{Definition}

"\newtheorem" is colored purple, but "\theoremstyle" is colored grey.

And in this segment
$$
A=\begin{pmatrix}
a_0 & 0 & 0 & 0 & \dots \\
a_1 & a_0 & 0  & 0 & \dots \\
a_2 & a_1 & a_0 & 0 &  \dots \\
a_3 & a_2 & a_1 & a_0 &  \dots \\
\vdots & \vdots & \vdots & \vdots & \ddots
\end{pmatrix}
$$

everything is colored brownish orange

bute here

$$
\T A =
\begin{pmatrix}
0 & 0 & 0 & 0 & \dots \\
1 & 0 & 0 & 0 & \dots \\
0 & 1 & 0 & 0 & \dots \\
0 & 0 & 1 & 0 & \dots \\
\vdots & \vdots & \vdots & \vdots & \ddots
\end{pmatrix}
$$

"\begin" is purple, "pmatrix" is blue, the numbers are black, and the 
ampersands are red.

Can anybody help me understand why this is the case?