The roast was frozen for about 3 weeks, defrosted in the fridge since Tues night, and it has no odor.
The roast is fine and you should cook it sooner rather than later. The discoloration is simply oxidation that is very common in red meat.
it should be fine as long as it wasn't like in the fridge for 5 or more days before you froze it.
Meat can be held in your freezer for up to 90 days. If it's really frozen it's going to take two days in the fridge to fully defrost anyway.