Unexpected results when drawing using colors with an alpha channel

When experimenting with colors with an alpha channel to draw a shadow for my watch hands, I get very different results on the simulator and the actual device (fr955). While the shadows are visible in the simulator, the device doesn't show any shadows on white background, only on black background (over the 9 o'clock tickmark in the image).

The code is straightforward, writes directly to the screen, and the blend mode is unchanged (default):

var shadowColor = Graphics.createColor(0x80, 0xaa, 0xaa, 0xaa);
dc.setFill(shadowColor);
dc.fillPolygon(shadowCoords);

Is this what has to be expected, at least on low-color devices?

Any tips how I can make this work better?

SIM vs Device

Andreas Huggel over 2 years ago

A workaround is to make the shadow color darker:

var shadowColor = Graphics.createColor(0x80, 0x77, 0x77, 0x77);

This works on the device as well, mapping the color to light grey on white background.

For lighter shades of grey, the simulator uses light grey but the device shows white on white background.