Hi Bob, I went back to see what I did and couldn't remember

but luckily, I had saved the file with all the layers in it!
It was quite simple really.
1. make a new layer and fill it with a dark pinkish color, set the blending mode to color.
2. using the polygonal lasso tool, make a triangle shaped selection over the lower right half of the layer.
3. choose "invert" under the Image menu (it's in one of the sub-menus). This turn the lower right a kind of bluish-green
4. make another new layer and fill it with a rich green set the blending mode to difference
5. using the polygonal lasso tool again, make a triangle shaped selection over the lower left half of the layer.
6. choose "invert" again
7. make an oval selection over the layer you made in step 4 and then choose "invert" again
8. keeping the same selection outline as step 7, make the layer from step 1 the active layer and invert again.
Hope this makes sense. I've attached an image showing the layers.
Margaret