QGIS » QGIS Application

That's a pretty big regression, affecting symbology. Under rule-based symbology, a given symbol's layers will be rendered as many times as the number of layers the symbol has. Which means that if a symbol has a non-opaque fill, that non-opaque fill will be rendered X times, with X representing the number of layers the symbol has.

Strangely enough, the regression only occurs under rule-based symbology. The same symbol rendered under simple symbol symbology works just fine.

1. Open the attached project
2. Open the Composer 1 window, and notice how the drawn polygons on the map are clearly much darker (incorrect) than the legend symbol (correct)
3. Go back to QGIS' main window, open the layer's property window, and open the one rule from the rule-based symbology panel
4. There, remove one of the Simple Fill layer, click on ok to close the symbol dialog, and click on Apply
5. You'll notice the polygon fill on the canvas gets lighter
6. Repeat again, remove another Simple Fill layer, and apply the change, you'll notice the polygon fill gets more lighter as you remove layers, until your left with your single fill layer, with the proper non-opaque color rendered.