Overriding the shade of color displayed

Each terminal emulator has its own way of setting color shades (or not). Xterm uses X resources, some of the newer emulators have dialog boxes, some have configuration files.

In Konsole, edit the color scheme in your profile (from the menu: “Settings / Edit current profile”, “Appearance” tab, select a color theme and edit it or make a new one).

There is a common control sequence to set the shade associated with a color number from the application: OSC 4 ; c ; spec BEL where OSC is ESC ], c is the color number and spec is a color spec such as #RGB.

printf %b '\e]4;4;#6495ed\a'  # set the blue shade to CornflowerBlue

A change by the application is only effective until the next terminal reset. If you use this method (only recommended if your terminal lacks a configuration mechanism), to make the change effectively persistent, append the color configuration escape sequence to your terminal's reset string (termcap: r1 string; terminfo: rs1 string).