The detailed description is here.

Added:

• the SetColorFormat(ENUM_COLOR_FORMAT aColorFormat=COLOR_FORMAT_ARGB_NORMALIZE) method;
• the parameter: aColorFormat - the ENUM_COLOR_FORMAT color format;
• in the Init() method the aColorFormat parameter is added.
  

In all methods of color setting the aA parameter is added, it has values from 0 to 255. 0 - transparent drawing, 255 - transparent. Default value is 255.

In the Stream.mq5 file (script) is given the example of drawing with transparency.