How to colour text inside aligned gb4e gloss examples?

Question

I am using the package gb4e to gloss a number of linguistic examples. Its main feature, is that it aligns the words in the original language with glosses.

I would like to be able to change the font/colour of some parts of the text so as to highlight those that are more important in a particular context.

Example. In the following example, the first line is how I currently imagine my ideal solution. Unfortunately, it does not work. The second line, instead, is my current solution: this works, but I have to repeat the command for every gloss and makes the source code less readable. The third line is a failed attempt to dodge the issue: grouping together several words doesn't work because it makes them part of the same gloss.

\documentclass{report}
\usepackage{color}
\usepackage{gb4e}

\begin{document}

\begin{exe}
\ex \glll
    a \color{blue} b c d \color{black} e f g\\
    a {\color{blue} b} {\color{blue} c} {\color{blue} d} e f g\\
    a {\color{blue} b c d} e f g\\

\end{exe}

\end{document}

output:

I am looking for a better solution which achieves the same result as the second line of the given example, but it does not make the source code so unreadable.

I am open to suggestions which do not involve the package gb4e, in case there exist better packages for dealing with this kind of situations.

---

edit: the ideal solution is something of the form

a \fromNowOnTextIsBlue b c d \fromNowOnTextIsBlackAgain e f g\\

that is, a way to change the colour "globally", so that it spans beyond the local scope. In fact, the package gb4e considers any command as a standalone gloss and thus it does not propagate its effect across subsequent words. Is that possible?

Answer 1

Here's a version which patches the cgloss4e glossing macros to add the colour of your choice. I've created three macros:

\glosscolor{} % sets the colour of the gloss elements
\clt  % turn colouring on 
\clf  % turn colouring off 

Since this modifies the glossing parser code, it will work with either \gll or \glll lines. It will not work in regular example lines. The colouring turns off at the end of each gloss line. This uses the xcolor package instead of the color package, so that the color changes can be made relative to the current document color.

\documentclass{report}
\usepackage{xcolor} % instead of the color package
\usepackage{gb4e}

\makeatletter
\newcommand*\glosscolor[1]{\gdef\@glcolor{#1}}
\glosscolor{red}
\AtBeginDocument{\colorlet{savedcol}{.}}
\def\@glosscolor{savedcol}

\newcommand{\clt}{\gdef\@glosscolor{\@glcolor}\color{\@glosscolor}}
\newcommand{\clf}{\gdef\@glosscolor{savedcol}\color{\@glosscolor}}

\gdef\getwords(#1,#2)#3 #4\\% #1=linebox, #2=\each, #3=1st word, #4=remainder
   {\setbox#1=\vbox{\hbox{#2{\strut\color{\@glosscolor}#3} }% adds space
                    \unvbox#1%
                   }%
    \def\more{#4}%
    \ifx\more\empty\let\more=\donewords
    \else\let\more=\getwords
    \fi
    \more(#1,#2)#4\\%
   }
\gdef\donewords(#1,#2)\\{\gdef\@glosscolor{savedcol}}   
\makeatother

\begin{document}

\begin{exe}
\ex \glll
    \clt a  b c d \clf e f g\\ % colour from a-d
    a  \clt b  c  d f \clf g\\ % colour from b-f
    a \clt b c d \clf e f g\\  % colour from b-d
\end{exe}

\end{document}

Answer 2

If you want to shorten \color{blue} to make your code more readable, then you can define a \newcommand to change it to something shorter, in this case I chose \cb, and you still get the same output that you wanted in the second line.

\documentclass{report}
\usepackage{color}
\usepackage{gb4e}

\newcommand{\cb}{\color{blue}}

\begin{document}

\begin{exe}
\ex \glll
    a \color{blue} b c d \color{black} e f g\\
    a {\cb b} {\cb c} {\cb d} e f g\\
    a {\color{blue} b c d} e f g\\

\end{exe}

\end{document}