Do not enter or change the source in the XML tab unless you really know what you are doing. There is a scripting editor provided so you can make these types of additions/changes. HIt Ctrl-Shift-F5 to activate the scripting editor (if it is not alraedy) or you can activate it under the Window menu. Now you need to highlight the object you want to affect (the checkbox). Then you need to choose an event you want to use for the object. In our case we want the Initialize event. This can be chosen from the Show dropdown (top left of the editor). Then at th eright side of the editor choose the language as Javascript and the RunAt to be client. Now you are ready to add your code. There is no provision in the Designer UI to change the checkmark
color so we have to do it in a weird way. These commands will do it for you:
var
f = event.target.getField("form1.Page1.CheckBox1")
f.textColor
= color.blue
The fieldname in quotes on the 1st line must be the path from the root to your checkbox object that you want to effect. Note that this is the AcroForm way of changing this and should only be used when absolutely neccessary.
Paul