Google will find you the answer. Print Hello world in red:
echo -e "\033[0;31mHello world\033[0m"
Explained
<esc><attr>;<foreground>m
<esc> = \033[ ANSI escape sequence, some environments will allow \e[ instead
<attr> = 0 Normal text - bold possible with 1;
<foreground> = 31 30 + 1 = Color red - obviously!
m = End of sequence
\033[0m Reset colors (otherwise following lines will be red too)
Look at http://en.wikipedia.org/wiki/ANSI_escape_code for full list of colors and other functions (bold etc).
The command tput, if available, will make life easier:
echo -e "$(tput setaf 1)Hello world$(tput sgr0)"
Can even save sequences in vars for simpler use.
ERR_OPEN=$(tput setaf 1)
ERR_CLOSE=$(tput sgr0)
echo -e "${ERR_OPEN}Hello world${ERR_CLOSE}"