Currently tooltips expose properties for changing the background color, format and visibility. Add more appearance options like color (Color property is already exposed), font, border width, border color and padding. For the time being the following workaround can be used:
	<style type="text/css">
		.k-tooltip
		{
			/*Sets border width and color*/
			border-width: 5px !important;
			border-color: Green !important;
			/*Sets padding*/
			padding-left: 5px !important;
			padding-right: 5px !important;
			/*Sets FontSize, FontFamily and color*/
			font: 15px Arial,Helvetica,sans-serif !important;
			color: Red !important;
		}
	</style>