How do I know if I should feed a colony in early spring or not?
There are two reasons to feed in the spring.
1. They are out of stores and starving, in which case I'd feed a heavy syrup or honey to give them something to eat. If you have some combs of honey you could put it in the middle of where the bees are hanging out on a day that they are flying. If you don't have full combs of honey, if you have PermaComb or some drawn comb, you could fill it with honey and and give it to them.
2. Stimulation. This is to stimulate them to raise brood. If you feed sugar syrup, especially thin sugar syrup, it simulates necatr which stimualates brood rearing. The problem with this is if they are short on stores they can use up all of the stores of honey and all of the stores of pollen quickly raising brood. You don't want to do this unless there are plenty of stores and it's close enough to acutal spring. I usually do this about a week ago or so here in Nebraska.
Not a simple answer.