High ISO noise red on D7000

Hi eveyone. I have a nikon D7000 and I take pictures of night skies with it. I have noticed that on my pictures (of course with high ISO 1250 - 5000) the noise was kind of red. I have checked on other nikon cameras and the D7000, D3000 and D5000 series have that "problem" but all the other do not. I don't know if any of you have noticed that but it is quite an annoying thing for me. I have send an e-mail to nikon asking if it was normal and they didn't seemed very interested. They told me that the other series where professionel so uncomparable...
What do you think about all that?
Thank you.