This baby is long discontinued, I got mine on ebay for about £10 (including shipping from the US) and i'm sure more are available on the net.
It's very difficult to describe this lip gloss properly. It is basically a clear gloss, but depending on the way the light hits it changes colour from blue to yellow to green to pink just like an opal. It's absolutely stunning. I have a gloss that i thought would be similar to this, Laura Mercier in Pink Quartz, but sadly while that looks holographic and perlescent in the tube (review of it to come later), it just becomes a pinky orangey colour on my lips whereas Clear Flash (number 310) really does colour-shift on your lips. Having said this it is the blue colour that seems to show up the most.
The gloss is not at all sticky in fact to me it feels almost oily. By that i mean it doesn't feel at all thick or greasy, it feels very liquidy and slippery, but it stays put well with no running or feathering. It does not have amazing staying power (but then i've never found a gloss that really does have great staying power) to me it seems no better or worse than the majority of my other lipglosses.
To get the best of the colour-shifting i find it's best to layer it on quite thickly. It applies with a doe-foot applicator, which is pretty standard practice. Personally i prefer a brush-tip, but i know lots of people find doe-foot applicators easier to use. I particularly like to put this on the top of coloured lipsticks and lip pencils to just add a chameleon colour effect to the lips. In order to do this i tend to first apply the lipgloss to the back of my hand and then pat it on my lips with a finger, simply because i don't want to contaminate the gloss by rubbing the applicator over dark or bright lipstick.
A quick word on the smell. I personally have no problem with most cosmetic smells unless it is truly overpowering, but i know that scent can be a big deal to some people. This gloss smells very odd to me. It is quite strong too, but i wouldn't call it overpowering. The smell is like... a synthetic candy mixed with vanilla. There's something toffee-apple-ish about it too. My girlfriend thinks it smells like 'a sweetened vegetable'. I personally neither like it or hate but scent is a very personally taste, however i can't smell it at all when it's actually on my lips and it doesn't really have any flavour, just a slight sweetness.
Here are some pictures, i've tried my best to capture the opalescent qualities.
Here is it in the tube:
in natural light:
and with flash:
And now on the lips:
Firstly on its own:
Here i have it over NYX Orange Soda (a pale, nudeish orange lipstick):
And here i am wearing it over Mac Magenta lip pencil:
In these photos you can only clearly see the lovely pale blue, but in real life you can see light greens, pinks and yellows too.
I would really highly recommend this lip gloss, if you can get hold of it and you can manage the bizarre smell (i don't find it unpleasant, just really weird). It's pretty unique and looks beautiful just on it's own, but can also add another dimension to any lip product you layer it on top of.