Assuming that MNP paint is the solid variety, i.e., not metallic or pearl, when I am not sure of the HSV components of the paint color which must be applied in the livery editor, I have approximated a paint color by testing decals applied above the desired color with unknown values.
Try loading one of the Nissans painted with MNP into the livery editor creating a new livery which you need not save. Apply a square decal above a paint workspace section which may be viewed from multiple angles and in the various ambient light conditions. Adjust the HSV components of the decal so that you cannot distinguish between the decal and the underlying paint. Record these values and use them in a new livery editor creation for paint for your R33.
I hope you find this technique useful 👍