Essentially, the colors of the legend markers are obtained automatically. Whenever the stroke of the line (representing the line series) changes, the legend marker should automatically get updated. In order to change the stroke of the line, you can chose from 3 different approaches:
1. Setting the Stroke property of the LineSeries directly.
2. Using a chart palette.
3. Using the StrokeShapeStyle property of the series to pass a style targetting a Path and using a Setter for the Stroke property.
The second and third option may be a little inconvenient in your case so I think that using the Stroke property of the LineSeries is the easiest way to go.
As for the axes - you can style the axes in more than one way. If you need the same color to be applied to the labels, ticks and axis line, you can use the ElementBrush property of the axis. If you need different colors for the different elements you can use the LabelStyle, MajorTickStyle and LineStroke properties of the axis.
I hope this information helps. Let us know how it goes.
Check out the Telerik Platform - the only platform that combines a rich set of UI tools with powerful cloud services to develop web, hybrid and native mobile apps.