I am about to install a new head unit into my KJ2 Verada.
As I want to be able to go back to stock if need be I didn't want to cut wires etc.

I noticed there are a few different ISO connectors. What are they each for?

I am ok to solder the head unit wires to the ISO connector, just want to be able to "plug & play" my original head unit later.

Depending on the head unit, you shouldn't need to solder anything.
Get a head unit to ISO harness (will vary from depending on stereo manufacturer/model) and a ISO to Magna/Verada harness and connect the two together.
Some head units have a ISO harness to begin with.

I have a Eclipse CD5030 head unit, which doesn't have ISO ends and Aerpro didn't make a harness for it. I got a Magna harness with no plug on the other end (AP7011), put bullet connectors on the end of that harness and the end of the head unit harness and hooked it up that way.
Made it super easy to hook up my Blackvue/Power Magic Pro as well, which runs off the stereo accessory and constant wires

http://www.ebay.com.au/itm/MITSUBISHI-CAR-RADIO-STEREO-ISO-WIRE-LEAD-HARNESS-LOOM-/280610799383?pt=AU_Car_Parts_Accessories&hash=item4155b4ff17

http://www.ebay.com.au/sch/i.html?_odkw=&item=280610799383&pt=AU_Car_Parts_Accessories&_osacat=131090&hash=item4155b4ff17&_ssn=deluxe-item&_trksid=p2045573.m570.l1313.TR1.TRC0.A0.Xradio+har ness.TRS0&_nkw=radio+harness&_sacat=131090&_from=R40

More than half the cost than if you bought it here...

Depending on the head unit, you shouldn't need to solder anything.
Get a head unit to ISO harness (will vary from depending on stereo manufacturer/model) and a ISO to Magna/Verada harness and connect the two together.
Some head units have a ISO harness to begin with.

I have a Eclipse CD5030 head unit, which doesn't have ISO ends and Aerpro didn't make a harness for it. I got a Magna harness with no plug on the other end (AP7011), put bullet connectors on the end of that harness and the end of the head unit harness and hooked it up that way.
Made it super easy to hook up my Blackvue/Power Magic Pro as well, which runs off the stereo accessory and constant wires

i did this as well with my VX400A, all the wires are matched to aftermarket colours which makes it easy.only hard bits were the park brake and reverse trigger wiring(which need to be wired to other things)

double post

I didn't want to buy the 2 ISO connectors as I felt they would take too much space up at the back.
I bought the ISO for Mitsubishi and I was planning on soldering the Kenwood plug that came with the HU onto the ISO plug making it plug and play.

Are the colors on the ISO plug the same as they are in the car?
ie, when soldering, do I just go by the diagram and use the colors for the Verada/Magna head unit?