I'm sorry,
I'm using RGB565 color format, Embedded Wizard 8.10 and it's running on my own hardware.
The strange thing is, that whole components, texts, images etc can be displayed with a custom opacity, but a filled rectangle are displayed with 0% or 100% (Rectangle.Color.alpha = 0; Rectangle.Color.alpha = 255; only two values which force a reaction) opacity but nothing between.