Is it possible to send mail to only watchers group when custom field updated to "Red_Flag"?

[Cloud]

Is it possible  to send mail to only watchers group when custom field updated to "Red_Flag"?

I have already installed script runner plugin but I can't find the suitable built-in scripts.

Thanks for your great support.

[Joshua Yamdogo @ Adaptavist]

You should be able to do this fairly easily. You could set up a script listener that responds to "Issue Updated" events. In the condition of that script listener, check to see if the custom field value is "Red_Flag":

import com.atlassian.jira.component.ComponentAccessor

// get the Custom Field Manager
def customFieldManager = ComponentAccessor.getCustomFieldManager()

// get a Custom Field Object
def textCf = customFieldManager.getCustomFieldObjectByName("Name of your field here")

// check custom field value, returns true if value is found
issue.getCustomFieldValue(textCf) == "Red_Flag"

Remember to change the script and put in your custom field name.

If the custom field value is "Red_Flag" the condition will return true and a custom email will send. You can set the "To issue fields" to the "Watchers" group so that it goes to the Watchers only.

[Cloud]

#1.If my customfiled type is multiple select list and then use the floowing code to place in custom field description:

<script type="text/javascript">

AJS.$("#customfield_11903 option[value='-1']").remove();

(function($)
{
new AJS.MultiSelect(
{
element: $("#customfield_11903"), itemAttrDisplayed: "label", errorMessage: AJS.params.multiselectComponentsError
});
}

)(AJS.$);

</script>

to convert to components filed type.

But I don't wnat to remove "None" from the multiple select lists.

How can I revise the code?

#2.My multiple select list should have option:

None,Red_Flag,Blue_Flag and White_Flag

and then use this built-in scripts to judge

if Trigger(customfield name) contain 

Red_Flag or Blue_Flag or White_Flag then send to watchers.

Do you have any suggestions ? Thanks for your great support!