Transparency option for token bars?

In the release notes, it says: Token bars and radial menu bubbles now have a transparency option via the color picker under Personalization & Display. Where is this, because I can't find it. I see the color picker... but I don't see a transparency option unless they mean the "clear" button, which I thought was a "cancel" button. And if that's not a "cancel" button, why isn't there a "cancel" option to undo changes??

I had that problem also. It's the horizontal gradient bar below the color picker that lets you choose the transparency level. 

Ah, I see. It's controlling a FOURTH parameter in the rgb setting that must be the transparency level. Got it.  Thanks. That wasn't obvious.  I suppose it was too much to ask for them to put "transparency slide" or some other text on it? (Rhetorical question :-) 

They appear to be moving to a universal color picker throughout the interface. Some of them have that slider. FWIW, any of the pickers that support the hex format of color definition: #RGB will also accept #RGBa, where you can input a final value to control the alpha transparency. 00 is fully transparent and FF is fully opaque. So a nearly transparent red value could be set on a token aura for example by setting the color to #FF000011, or a not fully opaque blue could be set by #0000FFEE. Confusingly, the new color picker uses rgba(R,G,B,A) for its definitions, where the scale of each channel is 0 to 255. That red in the previous paragraph being defined as rgba(255, 0, 0, 0.07). Same idea, slightly different terminology. Hopefully, as the different tools across the site all get facelifts, there will be One True Color Picker to Rule Them All.