Why isn't this align environment aligning?

Question

Lately I haven't been able to get the "align" environment to work properly, except on trivial examples. It was always a little finicky, but in the last few days it seems to have gotten much worse.

This isn't formatting properly on Firefox 23. (Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:23.0) Gecko/20100101 Firefox/23.0)

$$\begin{align} \color{green}{\exists \;x \in D \; : P(x) & = \exists \;x \in D \; \; ( \;x \in A \wedge P(x) \;) \tag{E = Existential}} \end{align}$$

Here's a screenshot:

Am I making some mistake that would be easy to fix?

[ Update: Asaf points out that the alignment tab symbol & is embedded inside the \green block, so that the constructions on either side have unbalanced braces. Changing

 \color{green}{… & …}

to

 \color{green}{…} & \color{green}{…}

fixes the problem:

$$\begin{align} \color{green}{\exists \;x \in D \; : P(x)} & = \color{green}{\exists \;x \in D \; \; ( \;x \in A \wedge P(x) \;) \tag{E = Existential}} \end{align}$$

Answer 1

Move the \color bit outside the align bit. It will work just fine.

$$ \color{green}{ \begin{align}\exists \;x \in D \; : P(x) & = \exists \;x \in D \; \; ( \;x \in A \wedge P(x) \;) \tag{E = Existential} \end{align}}$$