To quote a classic:
Is that trip really necessary?
On one hand the equipment itself introduces a lot of error, like is your camera calibrated? and what's the lighting like? On the other side you got the 1:1 colors being altered by fading, dust, mixing with funny things like diesel fuel or paint leftovers and so on. Then you got this nice effect I've seen some time ago that a paint is a perfect match in the natural lighting but not anymore in artificial lighting.
In the end I'd personally vouch for looking at different paints and experimenting and mixing - as opposed to looking for the best phone app as this seems to me a lot like a waste of time. But of course this ist just my opinion - good luck with your painting and have a nice day
Paweł