See "viewing volumes with freeview" in the tutorial:
https://surfer.nmr.mgh.harvard.edu/fswiki/FsTutorial/OutputData_freeview

When you view the aseg, aparc+aseg, or any other FreeSurfer segmentation volume, make sure that the colormap is not grayscale but "look-up table".

You can get the AD and RD from the other outputs:
AD = L1
RD = (L2+L3)/2

From: freesurfer-bounces@nmr.mgh.harvard.edu <freesurfer-bounces@nmr.mgh.harvard.edu> on behalf of Zeng, Qi <qi.zeng@icahn.mssm.edu>
Sent: Monday, November 22, 2021 5:24 PM
To: Freesurfer support list <freesurfer@nmr.mgh.harvard.edu>
Subject: [Freesurfer] Freeview grey matter, white matter and Tracula outputs
 

        External Email - Use Caution        

Hi, 

If I want to freeview fully segmented grey matter, white matter, and Tracula outputs, are the following commands correct to the request?

# to visualize the segmented cortical outputs
freeview -v mri/aparc+aseg.mgz
Question: why is one hemisphere brighter than the other? How can I adjust so that they are equally bright?

# to visualize the segmented subcortical outputs
freeview -v mri/aseg.mgz
Question: why is only one hemisphere showing and how to add the other one?

$ to visualize AD. RD, FA and color-coded each 
freeview -v dmri/dtifit_FA.nii
Question: I cannot find the nifti outputs of AD and RD (however, the stats generated). where can I find it? Is there an example of how to color-code them for freeview?

Thank you!
Best, 
Jackie