Waves,
I'm going to try my best to think this through.

Hubby buys the berries dried that he drops into low boiling water to plump up a bit.

I think that currants (of any color) might get same texture.
Which color is less sweet? The green? I'm not familiar with currents.

As far as the sourness, if we move away from berries, we could consider something like green plums, . . .
Help me think of fruit that is sour that is not citrus-y.

M.