Nicolas, documents go green when they have been downloaded on your device. They'll be yellow if you have an old version, but a newer version is available. Either way, the latest version will be downloaded and opened if you touch the entry, unless you're offline, in which case you'll get the old version or SkyDemon will tell you that you need to be online to view the document.
It should never be the case that nothing happens at all. That would be poor UI, and isn't the way SkyDemon is designed to work. Please contact our customer support if you can reliably reproduce an issue such as the one you're describing, as it would be a bug that needs investigation.