htop res & virt colors
The red color indicates that the amount of VIRT or RES memory is in the area of gigabytes. The light blue color corresponds to megabytes, and therefore white color means kilobytes.
This is, that the users has instantly a visual information, if he searches for processes, which consume a lot of memory. Notice that, the nice values (NI) are also red, when they differ from 0 for the same reason as above.