I take both my Templars and Psi Ops purple, with Reapers and Sharpshooters yellow, then I take beige for Skirmishers and brown for the Assault... This is because they serve similar functions for me so I was willing to let them share paired colours while still taking different shades of colouration.

SPARKS get grey, Specialists blue, Rangers green, Grenadier orange, Technical red, Shinobi white, Gunners black.

I find the Specialists having blue and Psi/Templars going purple matches their already present colours, red for the Technical because of fire, orange for Grenadier for the explosions, Ranger just makes sense to have green... The rest were whatever was left, I liked white for Shinobi over black because of Storm Shadow from the GI Joe cartoon.

I could have used pink for Sharpshooter, but since both Reapers and them largely serve the same purpose for me, I went with a shared colour.

For the curious, Long War of the Chosen is why I have this particular set of classes.

; Psi Operative
; Purple
+UnitColors=(SoldierClass="PsiOperative", MainColor=85, SecondaryColor=76, WeaponColor=85, WeaponCamo=-1, ArmorCamo=-1)

; SPARK
; Grey
+UnitColors=(SoldierClass="SPARK", MainColor=60, SecondaryColor=56, WeaponColor=60, WeaponCamo=-1, ArmorCamo=-1)

; War of the Chosen classes
; Purple
+UnitColors=(SoldierClass="Templar", MainColor=44, SecondaryColor=78, WeaponColor=44, WeaponCamo=-1, ArmorCamo=-1)
; Yellow
+UnitColors=(SoldierClass="Reaper", MainColor=78, SecondaryColor=87, WeaponColor=78, WeaponCamo=-1, ArmorCamo=-1)
; Beige
+UnitColors=(SoldierClass="Skirmisher", MainColor=3, SecondaryColor=2, WeaponColor=3, WeaponCamo=-1, ArmorCamo=7)

; Long War 2 classes
; Yellow
+UnitColors=(SoldierClass="LWS_Sharpshooter", MainColor=76, SecondaryColor=85, WeaponColor=76, WeaponCamo=-1, ArmorCamo=-1)
; Brown
+UnitColors=(SoldierClass="LWS_Assault", MainColor=49, SecondaryColor=36, WeaponColor=49, WeaponCamo=-1, ArmorCamo=-1)
; Blue
+UnitColors=(SoldierClass="LWS_Specialist", MainColor=35, SecondaryColor=75, WeaponColor=35, WeaponCamo=-1, ArmorCamo=-1)
; Green
+UnitColors=(SoldierClass="LWS_Ranger", MainColor=81, SecondaryColor=72, WeaponColor=81, WeaponCamo=-1, ArmorCamo=-1)
; Orange
+UnitColors=(SoldierClass="LWS_Grenadier", MainColor=73, SecondaryColor=82, WeaponColor=73, WeaponCamo=-1, ArmorCamo=-1)
; White
+UnitColors=(SoldierClass="LWS_Shinobi", MainColor=91, SecondaryColor=94, WeaponColor=91, WeaponCamo=-1, ArmorCamo=-1)
; Black
+UnitColors=(SoldierClass="LWS_Gunner", MainColor=94, SecondaryColor=91, WeaponColor=94, WeaponCamo=-1, ArmorCamo=-1)
; Red
+UnitColors=(SoldierClass="LWS_Technical", MainColor=70, SecondaryColor=79, WeaponColor=70, WeaponCamo=-1, ArmorCamo=-1)