can a glass slab bend different coloured lights by different amounts?
Yes, a glass slab bents different colored lights by different amounts. But after emerging from other parallel side these colored lights converge and no colorful effect is observed.
It is same like joining two prisms in inverted position as shown below:
If we join two prisms in the same way as they are shown in above figure the new shape will work as a glass slab and we will see the same white line emerging out from the other parallel side of the slab.