@begueradj Go into /etc/default/grub and change GRUB_TIMEOUT=10 to say GRUB_TIMEOUT=3, or whatever timeout you like and then run update-grub. You will then have permanently changed the Grub Timeout.

In theat same /etc/default/grub file, GRUB_DEFAULT=0 determines which is the default OS to boot. 0 being the first line, 1 being the second line etc.. If you change that, then run grub-update, it will change that option. That is, until you add another OS or update the kernel and get a new entry on top of the grub list. Manually changing options requires you to keep an eye on how those changed options effect grub when new items are added.

Changing the colors is a bit more complicated, so, I will have to look for the link to the how-to. I'll get back to you on that. Meanwhile, here's a link that might be helpful for you. It adds a bit more to the grub2 explanation:
http://ubuntuforums.org/showthread.php?t=1664134

If you make your changes ONLY to /etc/default/grub, or, to the folders in /etc/grub.d/ and then execute update-grub. It should add those changes to grub.cfg. Any changes made to /etc/default/grub are overwritten by update-grub.

There are 2 good Ubuntu postings on Grub2:

here:
https://help.ubuntu.com/community/Grub2

and here:
http://ubuntuforums.org/showthread.php?t=1664134

Or if your question is not answered, let me know. I'm hoping I understood what you were asking. And don't apologize, I often have to use a translator and have been disappointed at the results.