According to the plans drawn up by civil engineer Joseph B. Strauss, the bridge was to be painted in a standard grey, or black with yellow stripes if the Navy had had its way. However, the residents of San Francisco took a liking to the orange of the anti-corrosion paint. This earthy shade of orange complemented the backdrop of the surrounding hills and mountains and blended into the landscape. Joseph B. Strauss therefore decided to keep the bridge in this colour. The paint used is a protective coating and is known as ‘International Orange’[13].
For example, the distinctive red colour of the Golden Gate Bridge is due to the original use of a red-lead (Menninge) coating, which has now been replaced by acrylic paint.
https://de.wikipedia.org/wiki/Golden_Gate_Bridge
Originally, the paint of the bridge was Lead(II,IV) oxide
https://de.wikipedia.org/wiki/Blei(II%2CIV)-oxid