Is there any AMS TeX or LaTeX macro for background color in math-mode

Is there any way to display math expressions with a background color (highlight) using AMS-Tex or AMS-LaTeX . For example, using AMS-TeX/LaTeX, we can display a math expression in font color using \color[colorName]{mathExpression}.

UPDATE Using the answer from @werner, I tried $\frac{\colorbox{yellow}{$a-b$}}{c-d}$ to highlight only the numerator but the size of a-b is much larger than the demominator c-d even with the setting of \setlength{\fboxsep}{1pt} -in the preamble - as shown below. How can I get the desired output shown below:

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If you load xcolor, you can use \colorbox{<color>}{$<math content>$}. This uses a regular "framed box", so you can set the values of \fboxsep to decrease the border. – Werner Dec 2 '12 at 6:27
ams-tex is plain-based, not latex, so although it's feasible to concoct a method to include color, it's not trivial, and i don't know of any package that might do it. ams-latex, on the other hand, is based (as its name implies) on latex, so @Werner's suggestion is one good possibility. – barbara beeton Dec 2 '12 at 13:33
@Werner, thank you for providing this information. I thought \colorbox command is only for highlighting plain text in color. For example, \colorbox{yellow}{x^3} would highlight the plain text x^3 in yellow and not in math-mode as ‘x cubed’. Whereas, the font color command, e.g., \color{yellow}{x^3} would display ‘x cubed’ in math-mode with yellow font. Now, I know that, for \colorbox, we need to enclose the math expression with delimiter such as \colorbox{yellow}{$x^3$}. – nam Dec 8 '12 at 4:19
@nam: I've converted my comment into an answer, since it seemed to have satisfied your requirements. – Werner Dec 9 '12 at 8:22
@Werner, sorry I did not know at that time about marking a response as an answer. I have marked it as an answer now. – nam Jun 1 '14 at 22:20

If you load xcolor, you can use \colorbox. This uses a regular "framed box", so you can set the values of \fboxsep to decrease the border.

In most cases, text-related formatting of this sort also transfers to math-related content. However, a verbatim switch is sometimes required since boxing reverts back to text mode. As such, use

\colorbox{<color>}{$<math content>$}


and not

$\colorbox{<color>}{<math content>}$


Here's a small example in LaTeX illustrating the use of \colorbox together with a modification of \fboxsep:

\documentclass{article}
\usepackage{xcolor}% http://ctan.org/pkg/xcolor
\setlength{\parindent}{0pt}% Just for this example
\begin{document}
Here is \colorbox{blue!50}{coloured text} with a coloured \colorbox{green!30}{$f(x)$} function. \par \bigskip
\setlength{\fboxsep}{2pt}% No "border" around coloured box
Here is \colorbox{blue!50}{coloured text} with a coloured \colorbox{green!30}{$f(x)$} function. \par
\end{document}

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herbert voss wrote a good summary -- which may be read from CTAN [MathCol](mathCol) which is pretty clear (even to non-readers of german) sinc mirror.ctan.org/info/math/voss/mathCol/mathCol.pdf since all the examples come with source+typeset output. – wasteofspace Dec 9 '12 at 10:54
i find writing in this sort of medium very difficult. have to find all my typos within 5 minutes; failed with my previous own afaict). anyway, the link should be mathCol – wasteofspace Dec 9 '12 at 11:04