An electronic device such as a wristwatch may include a conductive housing. A corrosion-resistant coating may be deposited on the conductive housing. The coating may include transition layers and an uppermost alloy layer. The transition layers may include a chromium seed layer on the conductive housing and a chromium nitride layer on the chromium seed layer. The uppermost alloy layer may include TiCrCN or other alloys and may provide the coating with desired optical reflection and absorption characteristics. The transition layers may include a minimal number of coating defects, thereby eliminating potential sites at which visible defects could form when exposed to salt water. This may allow the electronic device to exhibit a desired color and to be submerged in salt water without producing undesirable visible defects on the conductive housing structures.