Gtk Change Font and font color for an application

Question

I am having one Gtk+ and C application in which i want to set the font to some XYZ font type and font color to blue, for all the labels and text in the application how can i do

Answer 1

I also wanted to change the size of the font (because in the windows I don't see any common way how to modify general GTKMM's font size, and user wants bigger fonts because he has small screen).

This works, when called before displaying window:

style = formatString( "style \"my-style\" { font_name = \"Mono %i\" } class \"*\" style \"my-style\"", fontSize);
gtk_rc_parse_string( style );

This is a way to 'create application setting' and apply it on the fly. By the way, class "*" means that all items will have this style applied.