buddy dun know abt this experiment ...... red colour changes to green......

frequency is a property of light source and thus is constant....... whn light passes thru a denser medium its speed decreases so wavelegth must cange.......

but colour is in fact an outcome of energy wave= hf..... and that doesnt change.... so it mustnt change.... maybe the buk has mentioned abt somethng more done in experiment....

atbest wat i can thnk of is little absorption of energy by glass slab... and this ud lead to excitation of electronsand while falling of releasin energythus increasin it... thus changing frequency.... and colour......

but this realy is a stupid illogical ans.. if ur considerin glass...........

dun know........ see the experiment again..... i thnk somethng is wrng thre

Cheers!!!!!