"what different does the color of a $1 chip make in a poker room?"
None.

"Is it because they have more of the old purple/blue chips than the yellow chips?"
Yes, it takes a lot of $1 chips for the poker room.

"Why wouldn't they buy new chips for the new poker room and create some excitement?"

Why spend the extra $ for new chips if you have plenty of old chips? New $1 chips would cost them more than $1 each.
What excitement? Only the few chip collectors that wondered in would be excited.