The color of the roof for heating doesn't change the required size of the system. When a system is properly sized for heating, sun load doesn't count as the sun isn't out in most places during the coldest part of the day, which is the nighttime. However, the insulation qualities of the old versus new roof could make some difference. But unless you have a combination roof/ceiling, you can always add insulation to the attic to make up the difference there.
When was the last time the equipment was serviced by a good company? Could be you've got an impending mechanical issue. As always, if you think you've got something unusual going on, call out a good, qualified HVAC company to investigate.
If YOU want change, YOU have to first change.
If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!