asciidoctor-epub3 How to change font color

Hello,

I am moving my epub building toolchain from [OCR -> HTML -> OpenOffice -> Amanuensis -> EPUB -> MOBI] to [OCR -> HTML -> Asciidoctor -> MOBI]

It works with satisfying results. The chapter title layout could be improved to move out of the pure magazine layout (title + author)
What annoys me more is the font color that translates to gray on the kindle. This is not the best for reading at night.

Is there an easy way to change the font color ?

Jmm