Actually you will see some variation in colors on steel components and springs depending upon the year and make of car the AFB was produced for. Some mopar carbs had red springs on the pass side linkage. Some AFBs had a green coating of some sort on some of the pass side linkage components. I have seen gold springs and some silver springs that appeared to be chromed or at least very shiney compared to most. I mostly deal with early 60s Pontiac, chevy, and mopar performance AFBs and all were silver cad and silver springs in my experience. Ed Giolma used to restore a few and he would have some of the pass side components done in gold cad because he liked the contrast mixed colors give you. I've done a few that way too. As far as the cad plating I am lucky because there is so much off shore drilling stuff made down here, and cad protects against salt spray better than zinc, that Houston has quite a few cad platers still doing business. I send my plating to an outfit called Delta Specialty Coatings in Houston.
http://www.deltaspecialtycoatings.com/