Try this:

#threadTree tr[data-properties~="T_24label1"] { background-color:    #fadbd8 
 !important; }

That is for the Important tag; repeat with other tags T_24label2, T_24label3 etc.

Help/Troubleshooting Info, Profile Folder, Open Folder, close TB, create a new folder named chrome, create a new document in chrome with a text editor, name it userChrome.css (userContent.css), Save as type: All files *.*, copy in the above code, change the colours as desired. Double-click toolkit.legacyUserProfileCustomizations.stylesheets to true in Settings/General/Config. editor, restart TB.

https://www.userchrome.org/download-userchrome-css.html

Thanks a lot, it works!

In order to bring the transition to completion I've one thing left:

1. threadTree tr[data-properties~="T_24label1"] {

 background-color:  #FF0000   !important;
 color: #FFFFFF  !important;
 border-bottom: 1px; solid #FFFFFF !important;  ---> this line in TB 115 does not work... it is necessary to make rows with the same background color more "visible"...

}

Thanks in advance.

@sfhowes, May I ask a question also? That works great, but how does one change the color when the item is selected? I would like some visual evidence of selecting an message. Thank you.

Thanks a lot, it works! In order to bring the transition to completion I've one thing left:

1. threadTree tr[data-properties~="T_24label1"] {

background-color: #FF0000  !important; color: #FFFFFF  !important; border-bottom: 1px; solid #FFFFFF !important; ---> this line in TB 115 does not work... it is necessary to make rows with the same background color more "visible"... } Thanks in advance.

To add horizontal lines in the Threads Pane, try this:

table[is="tree-view-table"] td {
     border-bottom: solid 1px blue !important;
}

https://www.elevenforum.com/t/thunderbird-115-css-customization.16320/post-319273

Another option to distinguish lines in the pane is zebra striping (code can be found on this and other forums).

@sfhowes, May I ask a question also? That works great, but how does one change the color when the item is selected? I would like some visual evidence of selecting an message. Thank you.

To change the background of selected, tagged messages, e.g. for Important:

#threadTree tr[data-properties~="T_24label1"].selected {background-color:orange !important;}

Brilliant! You have resolved the one thing that I missed from 102: the ability for background color. I am color-challenged and just changing text color doesn't work for me. Thanks so much.

Many thanks @ sfhowes!

Here follows a commented piece of my userChrome.css as reference:

/* Set border to draw lines apart */ table[is="tree-view-table"] td {

    border-bottom: solid 1px #FFFFFF !important;
    line-height: 1.50em !important;

}

/* Custom colors */

root {

 --treeitem-background-active: #FFFF00 !important;
 --treeitem-text-active: #000000 !important;
 --listbox-focused-selected-bg: #FFFF00 !important;
 --listbox-selected-color: #000000 !important;
 --treeitem-background-selected: yellow !important; 
 --in-content-item-selected-unfocused: RED !important;

}

/* Email marked with T_24label1 but no selected */ threadTree tr[data-properties~="T_24label1"] {

 background-color:  #FFB9B9 !important;
 color: #000000  !important;

}

/* Selected email marked with T_24label1 */ threadTree tr[data-properties~="T_24label1"].selected {

 background-color:#FF0000 !important;
 color: #FFFFFF  !important;

}

/* Email marked with label CUSTOM_LABEL */ threadTree tr[data-properties~="TCUSTOM_LABEL"] {

 background-color: #808080 !important;
 color: #FFFFFF  !important;

}

/* Selected email marked with label CUSTOM_LABEL */ threadTree tr[data-properties~="TCUSTOM_LABEL"].selected {

 background-color:#000000 !important;

}

Hope it could help other guys...

Cheers

For case also with description HOW TO SEARCH FOR THE LABEL TEXT.

/* Email marked with label but no selected */

1. threadTree tr[data-properties~="Timportant_5f_21_21_21"] {

background-color:  #ffe6e6 !important;
color: #000000  !important;

} /* Selected email marked with label */

1. threadTree tr[data-properties~="Timportant_5f_21_21_21"].selected {

background-color:#FF0000 !important;
color: #FFFFFF  !important;

}

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