Yesss! Now it works.
I tried many times, and I am a bit lost, but I think that it works best if it is in a html block, anyway after trying many times now I don't really know, so I left if both in the html block and the html footer. (such a rookie thing to do, but l will clean it later ).
It works nice, but it does something funny: on first load, on the first page you don't see the color, if you go to the second page, you see the color and if you go back to page one now you see it.
It would be nice to fix that bit, but so far it looks great.
Thank you very very much Vitaliksssssssssssssssssssssssssssssssss