Starting in version 15, markers can use the same color as the trace on which they connect.
For example, see a simple S-parameter graph with three markers. Notice the color of the marker text boxes is black.
Right-click on the graph and select Options, click on the Markers tab to display the dialog below. Click the Match text color to trace option to have the markers draw in the same color as the trace.
The markers will display as follows with the option checked.