Changing the color of colored outputs

Question

My terminal has a white background. When commands print yellow text to the terminal, I can't see the text clearly (due to low contrast). I thought: wouldn't it be great if all the yellow text that will ever be printed were transformed to brown text? That way, I can enjoy colored output without struggling to see the printed text.

Suppose a command wants to print yellow text. Is there a way to 'hijack' the escape sequence so that brown text is printed instead? Or is there another way to achieve color transformations?

Note: I'm using gnome-terminal on Ubuntu 18.04.

Answer 1

Many of nowadays terminals (including gnome-terminal) use two or even three color palettes: 8-colors, 256-colors, and 24-bits (roughly 16x10^6 colors). However, very often the first two sets can be chosen arbitrarily from the last one and again this is the case of gnome-terminal (and for example its cousin terminator).

Now, to change particular color palette choosing from 24-bit rgb palette we need \e]4 escape code followed by changed color code number and rgb color. In your case

printf '\e[33mTEST\e[m\n'           # first print "TEST" to see yellow text
printf '\e]4;3;rgb:b0/4a/00\e\\'    # now we change yellow to brown
printf '\e[33mTEST\e[m\n'           # test again

The yellow nickname is 3 and for brown I've arbitrary chosen b04a00. After this modification you will notice that all yellow text has changed, even the one printed earlier.