Unless you are using RAW together with fixed exposure and aperture settings, it is difficult to get consistent colours.
Even then you can have some difficulty with consistent colors.
Supporting what ultravanillasmurf just said above, I'm edger to find the comparison "Color Test" picture I made a very long time ago. I'm hoping it is still on an old HD because I could not find it in my archived data.
It is very similar to what ultravanillasmurf did above (see his link). For my card I used eight different standard colors (black, white, yellow, blue, red, green, orange, and purple) painted on white card into 2.5cm x 2.5cm squares creating a colored checkered board (sixteen squares). Two sets of eight colors side-by-side on the same card. I then photographed the card with direct outdoor sunlight (very clear day), outdoor complete overcast, using "Daylight" light bulb lighting, standard incandescent lighting, fluorescent lighting, and several other different other lighting sources. The results were remarkable because the colors appeared to be completely different at times! Did I mention that when I took the pictures, I also used two different angles - 90 and 45 degrees - for each lighting source as well as a few different camera settings.
I also wanted to do the same tests by spraying the entire card with a clear gloss. However, I never got around to doing this.
Studying colors is a tricky business.
As a side note, I would like to add one more thing to this topic. I have met a few people that restore WW2 combat vehicles, and most like to be as accurate as possible right down to the color of paint. One individual even used actual surplus WW2 American army green paint (olive drab) to paint the vehicles. This surplus paint was of the earlier war color, and he gave me some in a small bottle. Of course I compared this with most of model paints I had. None were a perfect match, but a few came close. I think the old Humbrol MC21 "French Artillery Green" came pretty close. Of course the color changes depending on the weathering and other stuff applied to the model - including any filters.
For those that use Vallajo paints, I find that Brown Violet (70.887) is pretty close, but not a perfect match, for the Humbrol MC21 "French Artillery Green".