Puedes hacer dos cosas editar la imagen y cambiarlos manualmente...
o cambiar el codigo antes de compilar.
En el archivo bodeplot.cpp las lineas de la 118 a la 129 cambiarlas por:
//colors dels simbols
//mirar fitxer /etc/X11/rgb.txt per veure colors possibles
peak_Point[0]->symbol()->paint()->set_brush_color(Gdk::Color("DeepSkyBlue3"));
peak_Point[1]->symbol()->paint()->set_brush_color(Gdk::Color("blue1"));
peak_Point[2]->symbol()->paint()->set_brush_color(Gdk::Color("blue4"));
peak_Point[3]->symbol()->paint()->set_brush_color(Gdk::Color("gold"));
peak_Point[4]->symbol()->paint()->set_brush_color(Gdk::Color("DarkOrange1"));
peak_Point[5]->symbol()->paint()->set_brush_color(Gdk::Color("red1"));
peak_Point[6]->symbol()->paint()->set_brush_color(Gdk::Color("red4"));
peak_Point[7]->symbol()->paint()->set_brush_color(Gdk::Color("DarkGreen"));
peak_Point[8]->symbol()->paint()->set_brush_color(Gdk::Color("green3"));
peak_Point[9]->symbol()->paint()->set_brush_color(Gdk::Color("chartreuse1"));
esto ultimo es mas facil y rapido.