opengl color quadrangle - c++

Question

i have a programm that creates a black border an white corner (quadrangle).
now i want to make the corner of the quadrangle in an different color.
i don't know where exactly to write the code, and i don't know much a but color4f, i searcherd on google, but didn't get it.
(is there a good description somewhere?)
#include <iostream>
#include <GL/freeglut.h>
void Init()
{
glColor4f(100,0,0,0);
}
void RenderScene() //Zeichenfunktion
{
glLoadIdentity ();
glBegin( GL_POLYGON );
glVertex3f( -0.5, -0.5, -0.5 );
glVertex3f( 0.5, -0.5, -0.5 );
glVertex3f( 0.5, 0.5, -0.5 );
glVertex3f( -0.5, 0.5, -0.5 );
glEnd();
glFlush();
}
void Reshape(int width,int height)
{
}
void Animate (int value)
{
std::cout << "value=" << value << std::endl;
glutPostRedisplay();
glutTimerFunc(100, Animate, ++value);
}
int main(int argc, char **argv)
{
glutInit( &argc, argv ); // GLUT initialisieren
glutInitDisplayMode( GLUT_RGB ); // Fenster-Konfiguration
glutInitWindowSize( 600, 600 );
glutCreateWindow( "inkrement screen; visual screen" ); // Fenster-Erzeugung
glutDisplayFunc( RenderScene ); // Zeichenfunktion bekannt machen
glutReshapeFunc( Reshape );
glutTimerFunc( 10, Animate, 0);
Init();
glutMainLoop();
return 0;
}

Answer 1

First of all, you probably want glColor3f. glColor4f also takes an alpha (transparency) value, which you probably don't care about yet. The range of parameters is 0 for no intensity and 1 for max intensity of red, green and blue. So you could do something like:
glColor3f( 1.0f, 0.0f, 0.0f ); // red
glVertex3f( -0.5, -0.5, -0.5 ); // this vertex is red
glColor3f( 0.0f, 1.0f, 0.0f ); // green
glVertex3f( 0.5, -0.5, -0.5 ); // this vertex is green
glColor3f( 0.0f, 0.0f, 1.0f ); // blue
glVertex3f( 0.5, 0.5, -0.5 ); // this vertex is blue
glVertex3f( -0.5, 0.5, -0.5 ); // since it wasn't changed, this one will be blue, too

Answer 2

Specify vertex color right before specifying the vertex itself, in the GL_POLYGON block.
However, I would recommend going for OpenGL 2.x instead of learning that old OpenGL 1.x stuff anymore. There you use VBOs (Vertex Buffer Objects) instead of glBegin/glEnd etc.