Still can't say it jumps at me... So the most probable explanation is that a red filter applied in Nik will give a very slight color shift. Unless you have a better one.
By the way, what I said was not meant as a criticism, neither of you nor your technique, but merely as an observation. The color cast does not "jump" either. It is indeed a "very slight" cast, as I said initially. The reason I noticed it is that I struggle with the same issue occasionally, especially when applying split toning (and even if both hues are the same, differing only in saturation amount). The problem gets compounded in printing, as the printer induces its own color casts.
I am not a color-space expert (and if Andrew Rodney, a.k.a. digitaldog, is reading this, I am sure he could provide a better explanation), but I believe it has nothing to do with the Nik red filter, but most likely to do with color spaces. Your image is in sRGB color space, meaning that the system is using RGB
colors to achieve grayscale values, not always succeeding with 100% accuracy.
Try a simple experiment: use any software that can desaturate the image. Push the slider all the way to complete desaturation and then back quickly and you will notice the cast better. If you use a color picker, you will then measure absolute grays in the completely desaturated image.
You image deserve the best printing and presentation you can get, so getting rid of even minor distractions should help.