some questions
 

1. is there a way to prohibit a program from writing data on the hdd?
2. can i have different icons on each gnome workspace and how?
3. how to untar to current directory?
"tar -xvvf blablah.tar.gz" does not work
"tar -xvvf blabla.tar.gz -C ./" does not work
in both cases, the files go into some strange random locations.
4. how can i change the way colors are displayed for different content in the xfce terminal? I used to have red for archives, blue for dirs etc. in kde, but lost all that after changing to gnome.

3. tar xvzf <file>.tar.gz should put it into the current directory.

Untar with:
You had a typo as -xvvf

You really should put unrelated questions in their own threads (with descriptive titles).

Regarding 1., you could mount the relevant partition read-only, but presumably that would cause some problems. Can you explain why you need to do this?

Terminal text colors are program dependent. For the ls command, you use ls --color.

actually, I'm using the exact same program as I used before only now it has no colors. With --color I get some colors, but not the same set I used before. Is there any place where I can edit how the colors are displayed?

Aliases
 

Linux distros and desktops always use some aliases. You can look at the man page for alias which is a command to create aliases. Then, when you run a command it will use the alias instead.

Example: make ls and alias for ls --color. Now, when you type ls it will execute the alias, ls --color. The terminal itself does not know file types, much less does it know how to make certain types one color and other types another color.

alias is a bash builtin so has no man page. help alias gives the bash builtin equivalent of a man page but does not give as much as the bash man page which includes the great sentence "The rules concerning the definition and use of aliases are somewhat confusing". :D