# Chemfig: \color doesn't work

Why \colordoesn't work? I need to color the -OH oxydrilic function:

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[italian]{babel}
\usepackage[
a4paper,
margin=15mm,
bindingoffset=2mm,
heightrounded,
]{geometry}

\usepackage{amsmath}
\usepackage{chemfig}
\usepackage[version=3]{mhchem}

\begin{document}
\schemestart
\chemfig{CH_3CH_2-[:-60,,3]C(-[:-120]H)=C(-[:-60]H)-[:60]H}
\arrow(.-1--){->[\chemfig{H_2O}][\chemfig{H^+}]}[,1.5]
\chemfig{CH_3CH_2-[:-0]C(-[:90]{\color{red}OH})(-[:-90]H)-C(-[:-90]H)(-[:90]H)(-[:0]H)}
\schemestop
\end{document}


• Have a look at the manual section 12.1 How to write a colored atom (p. 42 of the manual to v1.2e 2017-05-20) – clemens Jun 21 '17 at 20:10
• Unrelated to the question, but: version 4 of mhchem was released about two years ago so \usepackage[version=4]{mhchem} seems more appropriate (unless you have an outdated TeX distribution…) – clemens Jun 21 '17 at 20:23

Using \textcolor seems to make it work.

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[italian]{babel}
\usepackage[
a4paper,
margin=15mm,
bindingoffset=2mm,
heightrounded,
]{geometry}

\usepackage{amsmath}
\usepackage{chemfig}
\usepackage[version=3]{mhchem}
\usepackage{xcolor}
\begin{document}
\schemestart
\chemfig{CH_3CH_2-[:-60,,3]C(-[:-120]H)=C(-[:-60]H)-[:60]H}
\arrow(.-1--){->[\chemfig{H_2O}][\chemfig{H^+}]}[,1.5]
\chemfig{CH_3CH_2-[:-0]C(-[:90]{\textcolor{red}{OH}})(-[:-90]H)-C(-[:-90]H)(-[:90]H)(-[:0]H)}
\schemestop
\end{document}


Apparently, using {\color{red}{OH}} also makes it work, just by bracing the "OH". Alternately, so does {{\color{red}OH}}, with the double brace.

However, as noted by the OP, it would be desirable to get just the oxygen linked to the bond, and so (after consulting the manual against my better judgment :^) I came up with this, in which I use a | to separate the atom specification, and apply color to each, respectively, as in {\color{red}{O}|\color{red}{H}}.

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[italian]{babel}
\usepackage[
a4paper,
margin=15mm,
bindingoffset=2mm,
heightrounded,
]{geometry}

\usepackage{amsmath}
\usepackage{chemfig}
\usepackage[version=3]{mhchem}
\usepackage{xcolor}
\begin{document}
\schemestart
\chemfig{CH_3CH_2-[:-60,,3]C(-[:-120]H)=C(-[:-60]H)-[:60]H}
\arrow(.-1--){->[\chemfig{H_2O}][\chemfig{H^+}]}[,1.5]
\chemfig{CH_3CH_2-[:-0]C(-[:90]{\color{red}{O}|\color{red}{H}})(-[:-90]H)-C(-[:-90]H)(-[:90]H)(-[:0]H)}
\schemestop
\end{document}


• This behaviour is actually documented: section 12.1 How to write a colored atom p. 42 of the manual to v1.2e 2017-05-20 :) – clemens Jun 21 '17 at 20:10
• I noticed that adding the color effect, it changes the bind offset. How would I do if I wanted carbon directly bound to oxygen? – Salvo Matteini Jun 21 '17 at 21:26
• @SalvoMatteini I am not a user of the package to know the proper way, but this will, I think, give what you want: {\textcolor{red}{O\rlap{H}}} – Steven B. Segletes Jun 22 '17 at 0:10
• @SalvoMatteini -{\color{red}O}|{\color{red}H} should work – clemens Jun 22 '17 at 7:00
• @StevenB.Segletes using \llap/\rlap with chemfig should rarely if ever be necessary… – clemens Jun 22 '17 at 7:22