The darker upper tailights get their darkness from the inside black plastic (and not from the outside lens which is clear). I don't think Toyota Parts sells the 04-05 inside black plastic piece by itself. You'd have to buy the entire 04-05 tailight assembly for about $180-$200 each. If I wanted to make mine darker, I would probably just try spray painting it first. Another possibility is to just tint the upper part of the outside lens. But that would cut down the light emitted (what light is that anyway?).
It's full of reflectors for the backup light which gives directional light for the backup camera. (I'm 85% sure of it). EDIT: and I'm 85% wrong too. I just checked and the upper rear lights are simply reflectors for the red brake lights. Whew, glad that 15% doubt was there. ZC1 (Also I'm talking about a 2008 model)
what!!!??? the top tail lights are LEDs. there are brake lights! 6 RED LEDS on each side sit on a horizontal plane. they shine up and then that 45 degree shiny piece reflects through the rear of the lense. the blinker is under the stop lights (yellow bulb) the rear back up lights are under the turn signal (clear bulbs) and the running lights are on the bottom. (red bulb)
ebay is your friend! but is there a reason the link will not copy over? eh, just search prius tail light... i saw 2 sets of the 04-05 lights there.
Here's the link to the eBay 04-05 tail lights: eBay Motors: 2004-2008 Toyota Prius Taillights (item 110254236121 end time May-25-08 21:00:27 PDT) 8 bids so far as I write. It'll be interesting to find out what they eventually sell for.
I just noticed this on mine too! It’s an ‘04, it survived all this time until the end of summer here & now this.... I already have some replacements off an ‘07 since the right one had a flaky LED.