Ian A Davidson, great thanks! The problem was here:
1. instead of:
SetBkColor(hdcStatic,TRANSPARENT);
needed to write:
SetBkMode(hdcStatic,TRANSPARENT);
2. here I returned null brush:
return (INT_PTR)(HBRUSH)GetStockObject(NULL_BRUSH);
but needed to return valid background color:
HBRUSH BGColorBrush = CreateSolidBrush(RGB(230,230,230));
return (LRESULT)BGColorBrush;