TTM wave A column with 4 color in TOS

Because I understand you are trying to learn how to do this for your self I provide some guidance rather than a direct solution. The colors you have attempted to use are the same exact colors as used in the TTM_Squeeze indicator. So you will find the code provided with the following video contains your solution:

https://www.hahn-tech.com/thinkorswim-ttm-squeeze-watchlist/

Now I will copy a specific section of the code from that video here so you can see how the if/then/else statement is properly configured:

hist.assignvaluecolor(if squeezeHistogram >= 0 then
if squeezeHistogram > squeezeHistogram[1] then color.CYAN else color.BLUE
else if squeezeHistogram < squeezeHistogram[1] then color.RED else color.YELLOW);

Now compare that pattern with what you have attempted and you should be able to identify where you went wrong.

Writing code is not easy. It takes an incredible degree of attention to detail. Every single character in the syntax must be in the proper location. If you still can't work this out, you should go back to a solution with only 2 colors and practice that until you master it.

[EDIT] The author of this post requested the solution because they were not able to get it working. I will provide a 3 step solution which shows how to convert the squeezeHistogram colors to work on Wave A of the TTM_Wave indicator:

Step one:

replace the first section "hist.assignvaluecolor" with a new function: "AssignBackgroundColor"

This is the result of setp 1:

AssignBackgroundColor(if squeezeHistogram >= 0 then
if squeezeHistogram > squeezeHistogram[1] then color.CYAN else color.BLUE
else if squeezeHistogram < squeezeHistogram[1] then color.RED else color.YELLOW);

Step two:

replace all occurrences of "squeezeHistogram" with "waveA". (HINT: You can do this in any text editor using the "find/replace" function)

This is the result of step 2:

AssignBackgroundColor(if waveA >= 0 then
if waveA > waveA[1] then color.CYAN else color.BLUE
else if waveA < waveA[1] then color.RED else color.YELLOW);

Step three;

Now we assemble the pieces, combining the first line of your original attempt to the result from step 2:

plot waveA = TTM_Wave().Wave1;
AssignBackgroundColor(if waveA >= 0 then
if waveA > waveA[1] then color.CYAN else color.BLUE
else if waveA < waveA[1] then color.RED else color.YELLOW);