For this example, the organization representatives have agreed to include the following text in the messages they send out:

[Tour Guides]

Copy that text.

1) Click the drop-down menu in the message, and choose "Filter messages like this"

We don't want to filter new messages based on the sender, but rather the subject line.

1) Enter Name.
2) Click Create.

1) Check Apply the label:
2) Click Choose label . . . 
3) Select New label . . .

1) Check Never send it to Spam
2) Check Always mark it as important
3) Check Also apply filter to x matching conversations.
4) Click the Create filter button

Find the label in your label list in Google Mail. Hover over the name, and click on the little triangle that pops up.

From the Label name, select Label color, then click on the color (you can change this at any time).