How to display two different colors on two sides of a triangle?

[loginlog]

I have tried to do as this:

glColor3f(1.0f,0.0f,0.0f);
glNormal3f(a,b,c);
glVertex3f(...);
glVertex3f(...);
glVertex3f(...);

glColor3f(0.0f,1.0f,0.0f);
glNormal3f(-a,-b,-c);
glVertex3f(...);
glVertex3f(...);
glVertex3f(...);

but it doesn't work!who can help me!

[Bob]

Enable backface culling and draw the triangle two times, one with vertices in clockwise order and one with vertices in counter clockwise order. OpenGL's backface culling is based on the order of the triangle's vertices in screen space, not the normal.