From the names, fruit color would tell you whether a purple crossed with an orange, or a green. Unless the color was dominant. And you would have to wait until they were ripe to know.
If you recall the type of leaf on each plant, that would give you a hint sooner.
P.S. To make sure that no bees break in and cross-pollinate your seed crop next year, you could bag a few branches of each variety, and only save seeds from fruit on those branches. Fabric stores have plenty of light fabrics or fine meshes.
Once you had enough green tomatoes set on those branches, you could even remove the bag (and just pluck any more flowers that came out on them). If you have a long season, you might be able to re-use the bag on a second variety. Pick any green fruit and flowers before bagging.
One way to reduce cross-pollination is to plant something attractive to bees, with lots of flowers and nectar, between and around tomato plants. It gives them better targets than the tomato flowers, and rubs some pollen off if they hit the trap blooms between tomato #1 and tomato #2..
