Colons follow independent clauses, semi-colons link two independent clauses.
Now, right or wrong, the way I remember this is that a semi-colon can be used in place of a period
(i.e., Jeff got fired from work; they said he was absent too often.
Jeff got fired from work. They said he was absent too often.).
Colons are my guardians of the list, and they cannot take the place of a period.
(i.e., The factory produces baked goods: donuts, buns, and rolls.
The factory produces baked goods. Donuts, buns, and rolls).