Posted by Siegfried Kurz on Jul 18, 2019; 10:30am
URL: https://discuss.asciidoctor.org/asciidoctor-pdf-with-custom-style-problem-with-fonts-tp6992p7000.html

Hello Dan,
I was nearly giving up, then I found out:

This works:
cat resources/themes/hit_OK-theme.yml
extends: default
base:
    font-color: 00FFFF
heading:
    font-color: 0066CC

This does NOT work:
cat resources/themes/hit_ERROR-theme.yml
extends: default
base:
    font-color: #00FFFF
heading:
    font-color: #0066CC

When You look at my posts above, I've used the version with the leading #-chars.
According to the documention,  #0066CC should be equivalent to 0066CC

asciidoctor-pdf -V
Asciidoctor PDF 1.5.0.beta.1 using Asciidoctor 2.0.10 [https://asciidoctor.org]
Runtime Environment (ruby 2.6.3p62 (2019-04-16 revision 67580) [x86_64-linux]) (lc:ISO-8859-15 fs:ISO-8859-15 in:ISO-8859-15 ex:ISO-8859-15)

best regards from germany
Siegfried