The following is what I snagged from the Bogen Site on Gossen meters. It's in their FAQ section:
My Gossen meter gives me a slightly different reading than my in-camera meter. Which one is correct?
Because there are no International Standards on this topic, variances can occur. Gossen and most European photographic manufactures, calibrate their meters at 5600o Kelvin, a "Daylight" setting. Most Japanese manufacturers calibrate at 3400o Kelvin, a "Tungsten" setting. This 2000o Kelvin difference in color temperature causes a difference in readings of approximately 1 F-stop.
This is interesting as I use a Pentax spotmeter and a Gossen LunaPro for incident readings. Now if I am reading the shadows with my spotmeter and the color temperature seems to be a variable in the equation it would stand to reason that if I'm reading the shadow detail of a red object rather than a blue object the reading is going to be different for each even though the same amount of shadow light is there. This is in addition to the error caused by the meter trying to make everything 18% grey.
There is an interesting thread on PN that can be read here:
Would this only be an issue for chromes and not B&W? Gee and I just thought I had it all figured out!!