#!/usr/bin/tclsh

proc get_color {obj_name} {
   global a_color
   if { [info exists a_color($obj_name)] } {
      return $a_color($obj_name)
   } else {
      puts "Warning: $obj_name has no color!"
      return "transparent"   ; # return a default color
   }
}

proc set_color {obj_name color} {
   global a_color
   set a_color($obj_name) $color
}

set_color a1 green
set_color a2 yellow
set_color a3 red

puts "a1 has color [get_color a1]"
puts "a2 has color [get_color a2]"
puts "a3 has color [get_color a3]"