Ari, you also have to take into consideration the air pressures, air/paint mixtures, distance of the gun from the panel, angle of the gun, speed of the hand/gun, thickness of the coats, humidity/temp you'll be spraying in, etc etc...
With metallics the colour difference you can see, (if it came from the same tin) is normallly just how the metal flakes stand up, if sprayed at different pressures it can effect the way the flakes want to lay down.
Or, so I've heard
It might be fact, or it might be fiction, but in my (limited) experience, when laying down colour coats, I've done most of the layers as even as I could (but still had some small tigers stripes going on) then give it a 'blend' (for lack of a better/more technical word
) diagonally all over the areas/panels to blend them all intogether, get the flakes laying down the same. 99% of the time it ended up in a nice even looking colour!
And, agree'd with what wildss said, do all the inners, like you have been, then get the whole outside of the car ready to go. Mix up all your paint/thinners (how ever much you think you'll need) then its all at the same ratio's and measure out your hardener as you go. The whole car will be sprayed before you know it and it will/should all look the same.