If there's no way to save your rainbow streak after you lose a round, then why does it tell you to save it? There should either be a way made to save it, or else there should not be a statement. The way it is right now is very misleading and deceptive!
I can try next time I play and have a rainbow streak. It only happens when you lose on a level and have a rainbow streak built up. When you fail the level, it says "Save your rainbow streak!" and has a bar with the pop bottle/s on it, and the last one will shake and drop off the bar.
This “save your rainbow streak” means that you can buy 5 extra moves with 10 gold bars. So you won’t lose your streak (progress) when you actually win that level.
The screen that Yosca posted is NOT the same as the one I'm talking about. Hers is the screen I get whenever I lose a level WITHOUT having a rainbow streak. When there is a rainbow streak, it's like the description I posted above. I don't have a rainbow streak right now to be able to take a screenshot of the screen I'm talking about.
I couldn't get a screen shot, as it only stays on a few seconds while the bottle is dropping out of the bar. I can't see the top part of the screenshot that Yosca posted so I don't know if it might be the same as the screen I get AFTER the bottle drops off the bar.
When the bottle is dropping, you see save your streak. Then you get the option buy 5 extra moves 10 gold. If you do that and you play on, and win the level with those 5 extra moves the bottle is on the bar again.