It's just a small tweak that I found years ago in the old BSN forum during my first playthrough, and want to shared here due to the BSN forum actual state

the credit goes to translucentwolf for sharing this at first place

1- Open the Gibbed Save Editor http://social.bioware.com/project/4373/
I think the instructions are really simple, but MAKE A BACKUP OF YOUR SAVE FILE JUST IN CASE

2 - Load the save file that you want to edit

3 - Go to Raw tab
Squad > Player > Appearance > Morph Head > Open the Texture Parameters Coleccion

4 - Add the following entries
1) Name = EYE_Diff
    Value = BIOG_HMM_HED_PROMorph.IllusiveMan.HMM_HED_PROIllusiveman_Eye_Diff
2) Name = EYE_Spec
    Value = BIOG_HMM_HED_PROMorph.IllusiveMan.HMM_HED_PROIllusiveman_Eye_Spec

5 - Click on accept

6 - Now open Vector Parameters Coleccion
Rename the entry EYE_Iris_Colour_Vector  to  Emis_Color

7 - Click on accept

8 - Save the changes you have made and thas all

OPTIONAL STEP
The color of the "tech iris ring" will be the same as your Shepard's current iris color, to change the color, you'll have to modify the RGB values located in newly named Emis_Color entry, if you have no idea how to find the desired color use this link, just remember to put 0, before the numbers of the color that you desire

NOTE
Since the head morph of the default Shepard can't be edited this only works on custom faces (Thanks to Kanarus for sharing this)