The example one-liner will print:

count = 3
color = blue

• text='3 blue; 5 green' assigns some example text in the variable text
• [[ $text =~ ([0-9]+)" "(blue|green) ]] tests if the value of $text matches the extended regex ([0-9]+)" "(blue|green), that is:
  • [0-9]+ -- 1 or more digits
  • " " -- followed by a space; note: it was important to enclose this space in quotes
  • blue|green -- the color "blue" or "green"
  • The parts of the regex enclosed in parentheses (...) will be available in the BASH_REMATCH array, if the pattern match is successful.
• The group of commands chained after [[ ... ]] with && { ...; } will be executed only if the [[ ... ]] command was successful.
• The echo commands print the captured expression in the first and second parenthesized subexpressions (...), in this example a count and a color.

Additional tips:

• The entire matched expression is stored in ${BASH_REMATCH[0]}, in this example the value would be "3 blue".
• If the nocasematch shell option is enabled, the match is performed case insensitively. For example if the example text was "3 Blue", that normally would not match, unless you run shopt -s nocasematch first before performing the matching. (Clear the shell option with shopt -u nocasematch if needed.)