\def\xlstyamlvalue{\normalfont\xlstGetStyle{basic}\normalcolor}
% a dash only marks a list item outside of a value, a comment or a string
\begingroup\makeatletter
\gdef\xlstyamlbullet{%
  \lst@ifwhitespace\xlstIfPmode{\xlstGet{keywordC}{-}}{-}\else-\fi}
\endgroup
\lstdefinelanguage{lYaml}{
   basicstyle=\xlstGetStyle{keywordA},
   % '**' keeps comments, strings and keywords alive within the value
   moredelim=**[l][\xlstyamlvalue]{:},
   comment=[l]{\#},
   morestring=[b]",
   morestring=[b]',
   sensitive=false,
   morekeywords=[2]{true,false,null,yes,no,on,off},
   add to literate={-}{{\xlstyamlbullet}}1
}

\RegisterLanguage{yaml}{lYaml}