файл gtkrc называется. среди этих строчек:
fg[NORMAL] = @fg_color
fg[ACTIVE] = @fg_color
fg[PRELIGHT] = @fg_color
fg[SELECTED] = @selected_fg_color
fg[INSENSITIVE] = shade (3.0,@fg_color)
bg[NORMAL] = @bg_color
bg[ACTIVE] = shade (0.95,@bg_color)
bg[PRELIGHT] = mix(0.92, shade (1.1,@bg_color), @selected_bg_color)
bg[SELECTED] = @selected_bg_color
bg[INSENSITIVE] = shade (1.06,@bg_color)
base[NORMAL] = @base_color
base[ACTIVE] = shade (0.65,@base_color)
base[PRELIGHT] = @base_color
base[SELECTED] = @selected_bg_color
base[INSENSITIVE] = shade (1.025,@bg_color)
text[NORMAL] = @text_color
text[ACTIVE] = shade (0.95,@base_color)
text[PRELIGHT] = @text_color
text[SELECTED] = @selected_fg_color
text[INSENSITIVE] = mix (0.675,shade (0.95,@bg_color),@fg_color)