Ivan,
We decided not to use the Asciidoctor coloring in the default theme, going for a more conservative look. We're still deciding what to use in the final 1.5.0 release.
Until then, you can control the colors by tweaking the theme. There is an Asciidoctor theme included. You can enable it using the pdf-style attribute:
$ asciidoctor -a pdf-style=asciidoctor sample.adoc
You can specify a path to a custom theme directory using the pdf-stylesdir attribute. The themes are defined in a YAML file, as you can see here:
https://github.com/asciidoctor/asciidoctor-pdf/blob/master/data/themes/default-theme.ymlEach theme file must be complete at this point (it doesn't cascade to the default styles).
I hope that clears things up a bit.
-Dan