What does Color(1-4) mean?

When trying to set alpha for lines in a parallelcoords-plot I stumbled on the command:

lineobject(i).Color(4) = 0.5;

It works but I don't understand what the number "4" means? When trying different inputs I noticed that Colors accepts integers in the range 1-4 and 1-3 looks to be specific hues of red, green and blue. But what does "4" mean and why do I have to specify Color(4) to be able to set the alpha?

Answer 1

[Walter Roberson]

Those particular kind of graphics object accept a color specification which is in the form of a four element vector of doubles in the range 0 to 1. The elements are in the order R G B A. So Color(1) would be the red component, (2) would be the green component, (3) would be the blue component, and (4) is the alpha component.

Depending on the kind of graphics object, the fact that it accepts alpha components might not be documented.

Also, a number of the graphics objects that are not documented as accepting alpha expect uint8 values for the RGBA specification.