TYPO3 v8 has reached its end-of-life March 31st, 2020 and is not maintained by the community anymore. Looking for a stable version? Use the version switch on the top left.
You can order Extended Long Term Support (ELTS) here: TYPO3 ELTS.
red : *0.8 ("red" is darkened by factor 0.8)
#ffeecc : +16 ("ffeecc" is going to #fffedc because 16 is added)
The color can be given as HTML-color or as a comma-separated list of RGB-values (integers).
You can add an extra parameter that will modify the color mathematically:
[colordef] : [modifier]
where modifier can be an integer which is added/subtracted to the three RGB-channels or a floating point with an "*" before, which will then multiply the values with that factor.