[Walter Soyka]

You need to loop through each of the selected project items. This should do it:

// prompt the user for input
var Start = prompt ("Enter start time (in frames)",0);
var Length = prompt ("How long should the work area be?", 1);

// set an undo group so the user can revert the change if they make a mistake
app.beginUndoGroup("Change work area in selected comps");

// let's keep track of how many comps we modify, so we can report back at the end
var modifiedCompCounter = 0;

// step through each selected item in the project panel
for (var i = 0; i < app.project.selection.length; i++) {

// we only want to work on comps
if (app.project.selection[i] instanceof CompItem) {
var myComp = app.project.selection[i];
myComp.workAreaStart = Start/myComp.frameRate;
myComp.workAreaDuration = Length/myComp.frameRate;
myComp.time = myComp.workAreaDuration + myComp.workAreaStart; // note the "+ myComp.workAreaStart" here -- without this, the script only sets the correct CTI position if the work area begins at 0
modifiedCompCounter++; // increase our changed comp counter
}
}
// write the number of comps we changed to the Info panel
writeLn("Modified work area in " + modifiedCompCounter + " comp(s).");
// close the undo group
app.endUndoGroup();

I’ve added a few good practices: some comments so it’s easy to tell what’s going on, a check to make sure we only try to modify comps, an Undo group so the user can change their minds after they use the script, and a little Info panel notification about the change.

Please do ask questions on anything that isn’t clear. I’d be happy to help.

Walter Soyka
Designer & Mad Scientist at Keen Live [link]
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
@keenlive   |   RenderBreak [blog]   |   Profile [LinkedIn]

[Walter Soyka]

You could use sampleImage() in an expression to drive the Fill color.

As always, Dan Ebberts illuminates:
https://www.motionscript.com/design-guide/sample-image.html

Walter Soyka
Designer & Mad Scientist at Keen Live [link]
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
@keenlive   |   RenderBreak [blog]   |   Profile [LinkedIn]

[Walter Soyka]

I doubt anyone is testing CS5 (from 2011) with Mojave. If resetting your preferences or logging out and logging in via the Creative Cloud application doesn’t work, I do think staying on an older OS to run older software would be advisable.

Walter Soyka
Designer & Mad Scientist at Keen Live [link]
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
@keenlive   |   RenderBreak [blog]   |   Profile [LinkedIn]

[Walter Soyka]

There’s not a great built-in way to do this, but there’s a good third-party plugin:
https://www.redgiant.com/products/trapcode-3d-stroke/

Walter Soyka
Designer & Mad Scientist at Keen Live [link]
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
@keenlive   |   RenderBreak [blog]   |   Profile [LinkedIn]

[Walter Soyka]

Maybe you could do it with a Media Encoder preset that adds an image overlay as an effect?

I do think that providing a still and instructions — even a quickie 15-second tutorial on the process — would be the most fool-proof in the long run, though.

Walter Soyka
Designer & Mad Scientist at Keen Live [link]
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
@keenlive   |   RenderBreak [blog]   |   Profile [LinkedIn]

[Walter Soyka]

Looks like z-fighting:
https://en.wikipedia.org/wiki/Z-fighting

Do you have several layers that are all overlapping at the same depth?

Walter Soyka
Designer & Mad Scientist at Keen Live [link]
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
@keenlive   |   RenderBreak [blog]   |   Profile [LinkedIn]

[Walter Soyka]

You could do this with a script.

Save this code as “01-duplicateLayerPreserveName.jsx” in your Scripts folder. (The number is important to force it to the top of the list, alphabetically, so we can assign a keyboard shortcut to it later.)

// duplicate selected layers and rename dupes to match originals exactly

app.beginUndoGroup("Duplicate selected layers and preserve exact names");

if (app.project.activeItem instanceof CompItem) {
var renamedLayerCount = 0;
for (var i = 0; i < app.project.activeItem.selectedLayers.length; i++) {
try {
var originalLayer = app.project.activeItem.selectedLayers[i];
var newLayer = originalLayer.duplicate();
newLayer.name = originalLayer.name;
renamedLayerCount++;
} catch (err) {};
}
writeLn("Renamed " + renamedLayerCount + " layer(s).");
}

app.endUndoGroup();

Reload Ae, then Edit > Keyboard Shortcuts. Search the command list for “script” and find the “01-duplicateLayerPreserveName” entry. Assign it a keyboard shortcut, and then you can easily rename layers without incrementing their names. (Note that this can cause unexpected results if you’re using expressions that refer to layers by name!)

Walter Soyka
Designer & Mad Scientist at Keen Live [link]
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
@keenlive   |   RenderBreak [blog]   |   Profile [LinkedIn]

[Walter Soyka]

It might be “z-fighting.”

https://en.wikipedia.org/wiki/Z-fighting

Do you have multiple 3D layers at the same depth?

Walter Soyka
Designer & Mad Scientist at Keen Live [link]
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
@keenlive   |   RenderBreak [blog]   |   Profile [LinkedIn]

[Walter Soyka]

You don’t need the quotes at all. They just tell JavaScript that you’re passing a string literal. When you create your txt1 and txt2 variables, they’re already strings as far as the expression engine is concerned.

txt1 = thisLayer.name;
txt2 = thisLayer.name + " 0";
thisComp.layer("csv test - Sheet1.csv")("Data")("Outline")(txt1)(txt2)

Walter Soyka
Designer & Mad Scientist at Keen Live [link]
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
@keenlive   |   RenderBreak [blog]   |   Profile [LinkedIn]

[Walter Soyka]

I’ve used app.findMenuCommandId(), too, but it has a couple of important limitations:
1) It only works on menu commands.
2) It is dependent on your localized language.

Your feature request has my vote!

Walter Soyka
Designer & Mad Scientist at Keen Live [link]
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
@keenlive   |   RenderBreak [blog]   |   Profile [LinkedIn]