Labels printed by `\showlabels` are not blue

[vlasakm]

Consider the following example:

\fontfam[lm]

\showlabels
\label[sec:a]
\sec A

\bye

The printed label is black, evne though \showlabels defines the following font for printing the labels:

\_fontdef\_labelfont{\_setfontsize{at10pt}\setfontcolor{blue}\_tt}

First, this uses the luaotfload font attributes, which the OpTeX documentation marks as obsolete. Not sure if we want to change this.

Second, the coloring doesn't work and this is a problem in OpTeX's Lua code.