Hi Marc, unless I've got the wrong end of the stick, I think PGD15 does have the old behaviour, ie clicking a colour on the colour line changes a selected shapes gradient fill to the solid colour selected.

The replace colour popup only occurs when you have two or more shapes with different colours selected, or when a colour is dragged and dropped from the colour line onto a shape or selected shapes that have a gradient fill.

I believe this popup enhancement/feature was introduced in PGD9 and presumably to DPX around the same time.