https://www.telerik.com/kendo-jquery-ui/documentation/api/javascript/dataviz/ui/stock-chart/configuration/seriesdefaults.legenditem.area.opacity
seriesDefaults.legendItem.area.opacity - API Reference - Kendo UI StockChart - Kendo UI for jQuery
In this article you can see how to configure the seriesDefaults.legendItem.area.opacity property of the Kendo UI StockChart.
api referencekendo uilegenditemareaopacity