Is there a way to dynamically define a continuously varying colour gradient using GEM?

I'm only interested in greyscale, and have tried colorSquare, but find it quantises the colours too much - ie. I get stripes when the difference between greys is small.

I've looked down the GL_QUADS route with GEMglColor3f and GEMglVertex2f, but as you might expect I can't find a way of separating the colours - ie. the last GEMglColor3f called always colours all four vertices.

Am I missing something really obvious here?!

Or am I going to have to investigate glsl shaders....

Thanks.

Smooth shading is only possible if the smooth shade model is enabled by OpenGL which is accomplished by a call to glShadeModel(GL_SMOOTH). -- http://www.falloutsoftware.com/tutorials/gl/gl4.htm

Also I saw something somewhere talking about needing to set vertex normals for smooth shading to work properly, maybe.