The magnifier icon is displayed as shown below for some search forms added in the navigation menu depending on the selected search form styles.
You can change the magnifier icon color by adding the below CSS code in the Custom CSS option of Ivory Search plugin settings on the path Ivory Search -> Settings -> Settings
.is-menu path {
fill: #b2b2b2 !important;
}
You can change the color value #b2b2b2 in the above code to whatever you want to use by referring the following pages.