htmlize-use-rgb-txt

htmlize-use-rgb-txt is a variable defined in `htmlize.el'.
Its value is

t

Documentation:
*Whether `rgb.txt' should be used to convert color names to RGB.

This conversion means determining, for instance, that the color
"IndianRed" corresponds to the (205, 92, 92) RGB triple. `rgb.txt'
is the X color database that maps hundreds of color names to such RGB
triples. When this variable is non-nil, `htmlize' uses `rgb.txt' to
look up color names.

If this variable is nil, htmlize queries Emacs for RGB components of
colors using `color-instance-rgb-components' and `x-color-values'.
This can yield incorrect results on non-true-color displays.

If the `rgb.txt' file is not found (which will be the case if you're
running Emacs on non-X11 systems), this option is ignored.

You can customize this variable.