I have discovered quite noticable variances using color film depending on which of my flash units I am using. I am using a living room couch with lots of colors as a test subject. Flash units: Vivitar 283 and 2600, with and without Lumiquest diffusers. Provia 100 and Reala 100 film. The 283 produces more natural (to my eyes) colors. Especially with the Lumiquest in place. The 2600 pictures are considerably bluer and colder (without the Lumiquest; I will be testing it with the diffuser next). Same camera/lens, of course. I checked the specs. 283 is listed as 5500 degrees Kelvin. 2600 is listed as 6000 degrees Kelvin. I realize that these are old units. Perhaps the color temperature has changed over time, either the bulb itself, or the plastic cover. Can a 500 degree difference really make a noticable difference? I don't have a color temperature meter; that would be interesting! I am wondering if anyone has noticed similar effects. And if so, have you tried modifying the color temperature with a cc filter or whatever? Anyone have a handy chart with a filter vs. color temperature values? Someone recommended trying a Skylight filter with the 6000 degree unit. I may try it. I will appreciate your comments; thank you.