enable/disable toolbar icons

[#1]

Toolbar icons appear gray if the window has the wrong type:

 vs. 

how can I control this behavior for my own toolbars?

[#2]

@Jonas_Rinne 

[#3 · Accepted solution]

If a Toolbar Icon is linked to a Built-In command, it automatically gets the enable/disable functionality related to the respective command.
... even if the user chooses his own icon:

 

The easiest way to get a "dynamic" Icon into a user-defined toolbar: 
Got to View/Cutomize/Menus and Toolbars, and rightClick copy the original function and paste it into the user-defined Toolbar.

To get such Shortcut Icons into user-defined Add-Ins, one has to follow these steps shared by @Jeff_Perkinson 

Alternatively, one can edit the addin.jmpcust file manually.
The syntax is type="builtin":

<jm:command>
 <jm:name>TEXT TO COLUMNS</jm:name>
  <jm:caption>Text to Columns…</jm:caption>
  <jm:action type="builtin">COLS:UTILITIES:TEXT TO COLUMNS</jm:action>
 </jm:command>