Nothing can make MSB look attractive. It isn't post-modern at all. I'd call its style brutalist, akin to the towers of Centre Square. I'd take floodlighting for it over any other option.
It's a gray slab of concrete. Colored lights will make it look even more sickly. And nothing along the vein of neon will look correct on pre WW-II structures, which are the bulk of notable highrises in Center City that either aren't among the Trophy Towers or aren't already lit. Point out one to me from anywhere in the United States and I'll know I'm wrong.
When I say floodlight, I'm talking something similar to what you see on the Bell Atlantic Tower. Many of the city's older buildings, with their setbacks, would have an even more striking appearance at night with such a light scheme.
2000 Market Street, Ten and Eleven Penn Center, 1818 Market Street - these are more fairly modern buildings that can adapt to a more fairly modern lighting scheme. It wouldn't fly for older-looking buildings.