Why do LaTeX equations disappear in Keynote PDFs and how do I fix it?

Your only option in Keynote to make your equation text visible in it and a Print panel saved PDF is to introduce a suitable text color other than black or white.

The equation editor supports color equations by prefacing the equation with \color{X}, where case-sensitive color names are on pages 4 & 5 of the blahtex PDF manual:

Usage:

\begin{aligned}
\color{NavyBlue}\Delta{f}=\frac{\partial^2\ f}{\partial x^2}+\frac{\partial^2\ f}{\partial y^2}+\frac{\partial^2\ f}{\partial z^2}
\end{aligned}

About LaTeX and MathML support in Pages, Numbers and Keynote - Apple Support (IN)

When you state "LaTeX Editor" are you implying the use of Apple's built-in equation editor in Keynote and its associated limitations described in: About LaTeX and MathML support in Pages, Numbers and Keynote - Apple Support (IN) . The blahtex manual found as a link in the preceding describes what is supported in the equation editor.

Or you are deriving the LaTeX content generated by another source and pasting into Keynote as an image or PDF?

I'm not a heavy LaTeX user, so I'm not certain, but I don't think you'll have much of an option here.

l suspect that the text's color is embedded in the LaTeX definition, so LaTeX is specifically defining the text to be drawn in white, not simply an inversion of the background color. I know LaTeX has support for background and text colors, but I think they're fixed and there isn't a simple 'invert' option, which is why I think you're down to editing them manually.

The only place that Pages, Numbers, or Keynote show LaTeX as text is in the Equation Editor itself. Once the equation is added inline in these applications, it is a Pages object as MathML compatible with MS Word, and as a PDF stored internally as Data/equation-nn.pdf for backwards compatibility with older Apple application versions.

> Thanks again - if apple is listening, can you think about addressing this?

They're not necessarily listening here, but they do listen at: Feedback - Keynote - Apple