Gradient "miter" in OpenGL shows seams at the join
I am doing some really basic experiments around some 2D work in GL. I'm trying to draw a "picture frame" around an rectangular area. I'd like for the frame to have a consistent gradient all the way around, and so I'm constructing it with geometry that looks like four quads, one on each side of the frame, tapered in to make trapezoids that effectively have miter joins. 

The vert coords are the same on the "inner" and "outer" rectangles, and the colors are the same for all inner and all outer as well, so I'd expect to see perfect blending at the edges.

But notice in the image below how there appears to be a "seam" in the corner of the join that's lighter than it should be.  

Is this artifact somehow a result of the gradient slope that I don't understand? If I change all the colors to opaque blue (say), I get a perfect solid blue frame as expected.

Thanks!

![alt text][1]


  [1]: http://i.stack.imgur.com/2BdFa.png
Gradient "miter" in OpenGL shows seams at the join
===

I am doing some really basic experiments around some 2D work in GL. I'm trying to draw a "picture frame" around an rectangular area. I'd like for the frame to have a consistent gradient all the way around, and so I'm constructing it with geometry that looks like four quads, one on each side of the frame, tapered in to make trapezoids that effectively have miter joins. 

The vert coords are the same on the "inner" and "outer" rectangles, and the colors are the same for all inner and all outer as well, so I'd expect to see perfect blending at the edges.

But notice in the image below how there appears to be a "seam" in the corner of the join that's lighter than it should be.  

Is this artifact somehow a result of the gradient slope that I don't understand? If I change all the colors to opaque blue (say), I get a perfect solid blue frame as expected.

Thanks!

![alt text][1]


  [1]: http://i.stack.imgur.com/2BdFa.png