Being that you're using Responsive Forms, it's more difficult to provide any type of solution that will stand the test of time because Nintex has chosen to no longer support easy css / javascript changes. So, while I can provide a solution that works now, there is no telling if it will continue to work as I am not familiar with how they plan on changing things in the future (especially with Universal Forms / Rules around the corner).
So, if you upgrade, make sure that you TEST the Form before committing to it.
Now that we have that out of the way...
Here's the Form Controls in question:
Here are the settings on the Yes/No Control:
Now... Select the 'Save' Button and create a New Rule button in the Ribbon at the top of your screen:
The Rule Editor should open up from the Right Side of your screen. I have mine configured as seen:
The Copy / Paste javascript is:
(function(formControlCall, checkBox, opacityValue){
"use strict";
var formControlID = formControlCall.split("'")>1] || "";
var targetControl = sourceContext.find(">formcontrolid='" + formControlID + "'].nf-filler-control");
var internalElement = targetControl.find("nformcontrolid]oid]");
internalElement.css({opacity: ((checkBox) ? 1 : opacityValue)});
return !checkBox;
}("{Control:Self}", {someCheckbox}, .25));
Please Note: You will need to replace the bottom value {someCheckbox} with the Named Reference that shows in Red:
Resulting in the following looking reference in your formula.
Previewing the Form, you can see it with the checkbox left unchecked:
and Checked:
I hope that this helps. If you want to change the opacity, you can just change the numeric value that is in the 3rd argument position (which I have set to .25 initially). Opacity only ranges from 0 (fully invisible) to 1 (fully visible), so you can change the range 0, .01, .02....~1.00
Wow ... that's some reply ... I will give that a try ... I didn't know you could by JS in the "when" section but I can totally see what's going on..
Very elaborate solution...
If you're interested in learning more about the subject, I have written a detailed guide on how to utilize JavaScript inside of the Rule System here:
It's an incredibly helpful thing to know in situations such as this!