Usually, if the cab has a fair amount of dust in it, the new capacitor will be much brighter when compared to rest of the chassis. As in, will look newer.
Also, download a "cap kit" map for that particular chassis and check to see if the replacement capacitors match the capacitance and voltage values of the "cap kit". Also, all the replaced capacitors should be uniform. (They should look like they came from the same factory with the same looking casing. Usually Xicon bright blue.
I think thats what you mean anyways.