In the rulebook it says to "Resolve all results of a single color before moving on to the next..."
Example. I roll 4 dice. 2 roll blue and 2 roll white. Can I assign 1 blue and 1 white to TWO different artillery units? Or do I have 1 dead artillery and the whites don't count?
Yes, you must apply all blues before whites... so it could end up that you have 2 useless whites if there are no "damaged" artillery by the time you get to assigning whites (and assuming no other damaged units).
OK. Let's say they are both in the same row. Do I have to count both blues BEFORE I count ANY white die? So basically it would be 1 kill and the 2 white die are nothing.
If they are in different stances (rows) you can spread the damage evenly as you describe... But for each ROW you must eliminate one unit before applying any damage to another of the same row.