If the text on your terminal is too dark -- or if one of RGB components, usually blue, is too dark -- vtgamma allows you to apply a correction. This is usually useful on Linux console, as most graphical terminals supply more persistent means of adjusting colors; vtgamma is still helpful on those which don't, or if you can't cope with unfriendly settings such as xterm's. Not all terminals allow palette control (so vtgamma might not work for you), the palette might be lost when a program resets the terminal (so you may want to use PROMPT_COMMAND or PS1).