There is a "color" property for all the drawable element.
You should be able to change the color for the element from the popupped "color selection" panel.

You can define a variable with type "Object" if you want color change dynamically during run time:
For example: define variables with name "red,green,blue,color..." , type "Object"
and set
color=new java.awt.Color(r,g,b,t);
where r,g,b,t are value from 0-255 , corresponds to value for RED/GREEN/BLUE and transparent.
or set
red=new java.awt.Color(255,0,0);
green=new java.awt.Color(0,255,0);
blue=new java.awt.Color(0,0,255);
and set color=red;  or color=green ...etc.