How do I get a field to automatically select a value and change color based on another automatic field?

Question

Here is the situation:
I have a row on a form called Finding Risk Rating. In this row are four fields: Probability, Severity, Risk Rating, Color.
Probability is a drop down menu with the following values: 1, 2, 3, 4, 5
Severity is a drop down menu with the following values: A, B, C, D, E
Risk Rating is a field that I have a custom calculation script:
var riskRating = this.getField("Probability").value+this.getField("Severity").value;
event.value = riskRating;
So, when I pick Probability = 1 and Severity = D, Risk Rating will automatically change to 1D, etc. This works fine on the surface as far as I can tell.
The part where I am stuck, is the fourth field Color.
Ideally, I want Color to be automatically populated depending on the value of Risk Rating. For example, for 1E I would want it to say "YELLOW" and the field to change color to yellow. For 1A it would be "GREEN" with the color green, etc.
I tried doing an if else for all cases, but it never refreshes to the correct value. I then checked using app.alert to see what fields riskRating and colorRank are (see code below), and I noticed that riskRating never changes, even though the value in Risk Rating changes. Is there a way to order script(s) so that if I execute one, the other will follow? I'm new to scripting for forms and haven't done any programming in 10+ years, so feel free to rip my code in favor or something more efficient, or direct me to a good resource I can learn from.
Here's the basis of what I have for scripting on Color. It's brief because I wanted to test it out before writing every 'if else' statement.
var colorRank;
var riskRating = this.getField("Risk Rating").value;
if (riskRating = "1E") colorRank = "YELLOW";
else if (riskRating = "1A") colorRank = "GREEN";
else if (riskRating = "5A") colorRank = "RED";
event.value = colorRank;
app.alert("colorRank = " + colorRank + ", riskRating = " + riskRating);
Any help is appreciated. Thanks!

Answer 1

One problem is if more than one combo box item has the same number associated with it, you cannot simply set the export value to the corresponding number since they need to be unique (or the user interface behaves weird). One thing you can do is set up an object to associate a list item with a value, and look up the value in code when a list item is selected.
For more information, see: http://acrobatusers.com/tutorials/2007/js_list_combo_livecycle