Applying colours direct onto silver

When applying some colours direct onto silver I’m getting a brown/yellow reaction. Why is this?

When applying enamels that contain gold (such as ruby and pink) there is always a risk that they will turn brown or yellow if they come into direct contact with silver. Applying a coat of clear flux prior to the application of an enamel containing gold will solve this problem, however when using Champleve and Cloisonné techniques you may have a problem if the enamel comes into contact with the vertical walls of the cells that have not been completely coated with flux. A solution to this problem is to grind the clear flux very fine thus making it easy to apply to the walls of the cells. Reducing the particle size will give a slight loss of transparency but this should not prove to be a problem, especially if Opaque enamel is being applied on top.