Edit the CSS file to change the colour.
Where else would you want it to appear? You'd have to either eidt the plugin "Add Infobar" plugin, which would be a bit fiddly, or disable the plugin and then manually insert the code in a template where you want it. If you going down teh manual path, you should probably check out this one:
https://vborg.vbsupport.ru/showthread.php?t=123117 which is what this addon is based on.