We're doing the same the SDK is doing, see MainViewStyle.qml that is a "copy" of MainViewStyle.qml of the Ambience theme (hurray not). There there is a Image of background_paper.png on top of the color, if you open background_paper.png you'll see it's basically adding some alpha, so it is "by design" that the color you see is not the one you specified.
We're doing the same the SDK is doing, see MainViewStyle.qml that is a "copy" of MainViewStyle.qml of the Ambience theme (hurray not). There there is a Image of background_ paper.png on top of the color, if you open background_ paper.png you'll see it's basically adding some alpha, so it is "by design" that the color you see is not the one you specified.