Two ways i know to change font and color in code.
useadd_*_override
:
add_font_override("font", load("res://newfont.fnt"))
add_color_override("font_color", Color(1,0,0))
useset
:
set("custom_fonts/font", load("res://newfont.fnt"))
set("custom_colors/font_color", Color(1,0,0))