I am testing my new Sigma SD1 Merrill ... Color capturing wise, I don´t know what to think

Hi! I am an amateur photographer. I love taking photos, and I am trying to learn my path into the "aficionado" niche But at the moment, is a (loved, expensive, caring) hobby.
When I received my Sigma SD1 Merrill, I decided to do some experiments, resolution and color wise. My first results are the following:
My eye told me that the real color was ALMOST the one depicted with the Sigma SD1 Merrill. I compared the same Ibiscus flower with my Sony RX100 and Nikon D5100 cameras. The Sony RX100 is very good at approximating the real color (quite similar to Sigma SD1 Merrill).
I tried my best to configure the three cameras with the same ISO, Open, distance, no processing, etc.
Anyway, the Sigma SD1 Merrill did render a bit "too" red into the flower. Now, the wall, unfocused behind the plant, is white. But if you measure the resulting RGB in these images, you will notice that the Sigma SD1 Merrill injected more BLUE at them. The white is not "white" but "blueish".

I am aware that these are NOT best efforts to experiment in a controlled way: Light was provided solely by a cloudy sky, which could somewhat get clearer In the exact moment I took the picture, and I did not notice it. I will keep testing. If anyone wants to propose a different testing, or has any explanation for the different flower tones achieved for each camera, I am "all eyes"

This is taken with my new Sigma SD1 Merril. I compared it with my Sony RX100 and a Nikon D5100. The Nikon definitely changed the Ibiscus color into a plastic Shiny one.

Sony RX100 left, Sigma SD1 Merrill Right. Seems to be pretty close in color matching terms.

Nikon D5100 left, Sigma SD1 Merrill right. It seems the Nikon decided that the Ibiscus should be shiny yellow.

Nikon D5100 left, Sigma SD1 Merrill Right. Both cameras on ISO 100, F2.8 image not processed (other than cropping).