Their urine color do change. If you have them home, and in 4 days, urine color is NOT a medium yellow-orange color, then keep a log of the color.
As long as their diet is fine, they should be okay.
If their diet changes due to the long trip, their urine color can change. If they eat exotic weeds (wild weeds not grass), their urine color will change to a reddish color.
Remind you that whatever pellet that man is feeding them, you should mix it 50-50 with the pellet you are feeding, or else the rabbit may reject the new pellet and it'll change their stomach condition because they are not used to the new one. (In some cases, I have read, you can kill the rabbit if their stomach doesn't agree with the change of pellet.)
You then mix more of your to less of the other guy's pellet. 70 - 30. Eventually move to 100%.