\font\large=cmr10 scaled \magstep4
\large
\def\blue{\HINTcolor
   {fg {0 0 0} bg{0 0 1 0.4}}}
\def\red{\HINTcolor
   {fg {0 0 0} bg{1 0 0 0.4}}}
\def\green{\HINTcolor
   {fg {0 0 0} bg{0 1 0 0.4}}}
\def\TeX{\hbox{\blue T}\kern-.1667em\lower.5ex\hbox{\red E}\kern-.125em\hbox{\green X}}

The colors of \TeX

\bye