Let agree to disagree.
Exually because linux always reports the memory to be full it’s shows useful information:
green on the bottom : memory allocated to the kernel (cutting some corners here )
red : memory used by applications (EDIT: the allocated memory to the apps is missing in this graph )
blue : buffers and cache
green on top : free (“headroom” before swapping more pages)
In general i really start to worry if the red line (=kernel + apps) uses more then 50% in a idle state;
if there is a lot of disk I/O even on more then 25%.
EDIT 3 : I admit it’s with nethserver-arm in mind, where memory resources are limited and leaking apps/drivers are not that uncommon…