On this page of the "Colors and line styles" dialog (which can be opened using the corresponding button 
in the toolbar at the top of the main window), you can set the various options for the display of the X-ray spectral lines at the position of the mouse cursor. Line 1 is always displayed at the position of the mouse cursor, lines 2-5 around this anchor position depending on their relative wavelengths compared to the one of line 1.
Note: You can toggle the displaying of the X-ray spectral lines on the Graphics page of the Options-dialog.
You can define up to a maximum of 5 spectral lines to be displayed around the position of the mouse cursor. The displaying of each of these 5 lines can be toggled by clicking on the corresponding checkbox in the "Display" column on the left hand side of the dialog.
For each of the 5 lines, the current color is displayed in a corresponding box. By clicking on this color box you can open a color selection dialog where you can select/define a new color for the corresponding spectral line.
The wavelength for each spectral line can be set either by selecting the corresponding radiation type in the drop down box in the column "Wavelength". As an alternative, you can also use any wavelength of your choice by first selecting the option "User defined" from the wavelength drop down box, and then entering/modifying the wavelength value in the input line to its right.
Finally, a short title can be displayed at the top of each line (at the top of the diffraction pattern). You can enter/modify the corresponding title string separately for each line in the input line on the right-hand side.