Reveal each bullet by opacity in Keynote 6.6?
This is what I tried and it worked in Keynote 6.6.1 (2560):


Create Bullet points text.
Select all bullet points and Copy 
Select all
but the first bullet point and set color to 10% white (or whatever you like) leaving the first line at 100%.
Paste the saved bullet points over the existing and align precisely.   
Apply the following setting to the newly pasted bullet points:




Using the Animate tool and the settings in the Build In automator Appear, the first bullet point will present in full 100% luminance with the succeeding points dim. As you click, the bullet points will appear as you have shown in your example.