this plugin make a css file in (plugin) directory. but plugin is necessary in any way… only if wordpress make a function inside admin panel is possible to replace plugin with custom css code without plugin. otherwise, if u make a simple file with code via ftp, u neet to edit theme manually or to make a plugin to insert code in header and include css file. with this small plugin u have color syntax, css file and no theme edit require (no ftp, never)!
i think, is a good plugin (not simply, another plugin).