It looks like this:
It's from the 'Go Blonder' collection by John Frieda, however this is the only product from that collection I have tried as I've heard some terrible things about the shampoo and conditioner such as FleurDeForce on YouTube who had an allergic reaction to them! Anyway, I love the spray :) It's saved me a load of £££ as I haven't needed to go back to my hairdressers for highlights!
How does it work? Basically, you spray it onto wet hair and then blow dry your hair. The product is heat activated so the more heat you apply, the blonder you'll go (theoretically). I rarely straighten my hair so I've just been spraying this on my roots maybe once a week and blow drying it and I can definitely see a difference! I usually just spray it on the top of my hair, as I usually wear it down so the under bits don't matter so much.
To prove it works, I have taken a picture of my hair normally and then lifted up so the roots underneath are visible and you can see how much brown regrowth I should have had over my entire head.
As you can see, I would have needed at least one lot of half head highlights to cover this, if not two lots.
Overall, I think this product is great if you need to touch up your roots without needing to spend a tonne of money. I wouldn't recommend this for dying all your hair, and it's always best to go to a hairdresser if you want to go blonde from a drastically different colour. However, if you just want to lighten your hair slightly - then this is for you! It's so much cheaper than the hairdressers - I'd much rather pay £6/£7 for this than £40 odd for half head highlights!
Hope this first review was okay, comment if there's anything you think I can improve and let me know if you have tried this product and whether you love it or hate it!