While creating a simple product shot for selling one of my lenses I recently noticed a quite visible color difference between the two speedlights I have been using:
After this experience I wanted to examine this more closely and created a simple test setup to compare the colors of the four different speedlights I own. To do this, I placed a greycard in front of the camera and fired each flash onto this greycard with different output levels dialed in. For each output level I took 3 subsequent shots so that I could also get an insight on the consistency between shots. First things first: For each output level all tested speedlights are very consistent. So I will only focus on the remaining aspects now. This is an overview of the collected photos:
As visible from the photo grid, the two Yongnuo speedlights are quite consistent with respect to color temperature. However, the Nikon and Metz ones are a bit warmer. Moreover, it looks a bit as if their color varies with output levels. This somehow contradicts what David Hobby said…
To be at least a bit more precise about the differences in color, I also include the histograms for the first photo of each speedlight. The measurement point in all cases (for the percent values Lightroom displays) was chosen in the center of the image.
At least now I know which speedlights to combine in case of a comparable product shot.