You can configure the theme options in the [hosted login page] (https://manage.auth0.com/#/login_page), in Auth0Lock, as:
var lock = new Auth0Lock(config.clientID, config.auth0Domain, {
(...)
theme: {
authButtons: {
"testConnection": {
displayName: "Test Conn",
primaryColor: "#b7b7b7",
foregroundColor: "#000000",
icon: "http://icons.veryicon.com/ico/Emoticon/Chat/away%20girl.ico"
},
"testConnection2": {
primaryColor: "#000000",
foregroundColor: "#ffffff",
}
}
}
(...)
});