How to use drawBitmap2 and tintColor ?

Hello,

I'm trying to use drawBitmap2 to tint and draw a greyscale png icon.

I created the greyscale PNG icon using GIMP, saving it using greyscale+alpha (I tried 8bit GS+A and 16bit GS+A, I also tried without alpha).

I declared it like using :
<bitmap id="sunriseIcon" filename="png/sunrise6.png" scope="foreground" />

I tried to draw+tint it in onUpdate() using :
dc.drawBitmap2(_screenCenterPoint[0], _screenCenterPoint[1], _sunriseIcon, { ":tintColor" => 0x55ffff });

The icon is draw, but never tinted... what am I missing here ?

Thanks for your help.

Nicolas.