Carbon dioxide is an acid, so the indicator changes color.
sublimnation is nothing but the dry ice changing form solid to gas HOWEVER the real answer to the question is the change from a neutral or base to an acid. The colour change is caused by an additive found in the indicator or cabbage juice this is called Anthocyanins. it reacts with the change in the PH level thus changing the liquid different colours. the reason it changes to orange/red when you add dry ice is due to co2 being an acidic gas.