Diana,
Sure you can set the selection color by using the Edit default symbology link at the bottom of the widget configuration UI (if you are using symbology from defaults for "Layer Symbology"). If you have the Layer Symbology set to "from server" then you do not have control of the selection color as it is obtained from the server directly. If you choose "from layer" then you can choose "Add/Edit Layer specific symbology" then you can choose the selection symbol for this specific layer.
Diana,
Sure you can set the selection color by using the Edit default symbology link at the bottom of the widget configuration UI (if you are using symbology from defaults for "Layer Symbology"). If you have the Layer Symbology set to "from server" then you do not have control of the selection color as it is obtained from the server directly. If you choose "from layer" then you can choose "Add/Edit Layer specific symbology" then you can choose the selection symbol for this specific layer.
Thank you, Robert!