Special effect with Keynote build in

Yikes! I can't remember how I created an certain effect in Keynote (7.3.1). I hope somebody can help.

Last year I created a slide in Keynote with the following effect:

• I created a bulleted list inside a text box

• I used a build-in effect (Fade and Scale) to have each bullet line appear one-by-one

• Each new line of text appears in pure bright white

• As each new line of text appears the text in the previous line changes to gray, so the audience's attention is focused on the latest line of text. Previous lines are still visible but are kind of dim.

For the life of me, I can't remember how I created that last effect (changing previous lines to gray). I've been playing with Keynote, I searched these forums, and searched other sites online, and couldn't find an explanation of how to do that.

Are there any Keynote gurus out there who can remind me?

Thanks much in advance for any/all help!