man page says:
-prettysrc
show HTML source view with lexical elements and tags in color.
However
$ lynx -prettysrc index.html
does the same as
$ lynx index.html
until one hits "\".
$ lynx -prettysrc -source index.html
is the same as
$ lynx -source index.html
So perhaps explain more on the man page, lest the user's expectations
not match what you had in mind.
P.S. Users are only allowed to see colored output inside lynx.
They are given no way to get it on stdout.
P.S., I note
$ lynx -preparsed -prettysrc index.html
ignores -preparsed