Subject: Why does a Red Cabbage indicator turn acidic ?

I created a red cabbage indicator and I left it out on my desk by a lamp 
(~50 cm away).  And within two days it had turned a pinkish red.  I tested 
it and the indicator still works and therefore it is an acid.  Why is it 
that it turned acidic, was it because it was in the light, or was it 
because of something else.  Thank you for your time.

Re: Why does a Red Cabbage indicator turn acidic ?