Set a coloured text and send it to the clipboard
As I do not have access to the web app you are using, I really cannot test if this will work for you.

The example AppleScript code, shown further below, with limited testing works for me as coded under macOS High Sierra.

Overview: Gets the selected text in Google Chrome and places it on the clipboard in the chosen color as HTML data, and pastes it back over the selected text.1 

It uses an Automator Service, set to Service receives selected text in Google Chrome, with [] Output replaces selected text left unchecked, to which a keyboard shortcut was assigned in System Preferences > Keyboard > Shortcuts > Services as: ⌃⌘C

The Automator Service uses a Run AppleScript action with the default code replaced entirely with the example AppleScript code.

Usage: After selecting text in Google Chrome then pressing ⌃⌘C a choose from list dialog box is shown where you can select which color to make the selected text on the clipboard. You do not need to use the mouse, just keystrokes, e.g. G-Enter for green, O-Enter for orange and R-Enter for red, or Esc to cancel the action.

At this point, if all works right, the selected text will have been replaced with the colored text from the clipboard.1 (You will have to give it a second to let the service complete.)

Yes, it's a few keystrokes, but once comfortable with it I believe it will become second nature and be faster then having to reach for the mouse, etc.

The usual caveats may apply for the use of this in: System Preferences > Security &amp; Privacy > Privacy > Accessibility 

1Also note that the text box containing the selected text must allow pasting back the same HTML class data type and structure that was placed on the clipboard as given in the comments to the OP as answers to the questions I asked, otherwise this will not work as coded. 



Example AppleScript code:

--  # Green HTML Color: #27ae60     '23323761653630'
--  # Orange HTML Color: #e67e22;       '23653637653232'
--  # Red HTML Color: #d35400       '23643335343030'
--  # sed command 'placeholder'     '706C616365686F6C646572'

property myBrowser : "Google Chrome"

property greenHTML : «data HTML3C6D65746120636861727365743D277574662D38273E3C7370616E207374796C653D22636F6C6F723A233030666630303B223E706C616365686F6C6465723C2F7370616E3E0A»
property orangeHTML : «data HTML3C6D65746120636861727365743D277574662D38273E3C7370616E207374796C653D22636F6C6F723A236536376532323B223E706C616365686F6C6465723C2F7370616E3E0A»
property redHTML : «data HTML3C6D65746120636861727365743D277574662D38273E3C7370616E207374796C653D22636F6C6F723A236433353430303B223E706C616365686F6C6465723C2F7370616E3E0A»

property tmpHTMLdata : "/private/tmp/tmpHTMLdata"


on run {input, parameters}
    activate me
    set selectedText to item 1 of input as text

    set chosenColor to (choose from list ¬
        {"Green", "Orange", "Red"} with title ¬
        "Color Chooser" with prompt ¬
        "Which color to make the selected text?") as text

    if (chosenColor as text) is "false" then
        return
    else if chosenColor is "Green" then
        my writeToFile(greenHTML, tmpHTMLdata, true)
    else if chosenColor is "Orange" then
        my writeToFile(orangeHTML, tmpHTMLdata, true)
    else if chosenColor is "Red" then
        my writeToFile(redHTML, tmpHTMLdata, true)
    end if

    do shell script "sed -i '' -e 's|placeholder|" &amp; selectedText &amp; "|' " &amp; quoted form of tmpHTMLdata
    set the clipboard to (read tmpHTMLdata as «class HTML»)
    delay 0.25
    tell application myBrowser to activate
    delay 0.25
    tell application "System Events" to keystroke "v" using command down
end run


on writeToFile(theData, theFile, overwriteExistingContent)
    try
        set theOpenedFile to open for access POSIX file theFile with write permission
        if overwriteExistingContent is true then set eof of theOpenedFile to 0
        write theData to theOpenedFile starting at eof
        close access theOpenedFile
    on error eStr number eNum
        try
            close access file theFile
        end try
        display dialog eStr &amp; " number " &amp; eNum ¬
            buttons {"OK"} default button 1 ¬
            with title "File I/O Error..." with icon stop
        return
    end try
end writeToFile




Note: The example AppleScript code is just that and other than any included error handling does not contain any additional error handling as may be appropriate. The onus is upon the user to add any error handling as may be appropriate, needed or wanted. Have a look at the try statement and error statement in the AppleScript Language Guide. See also, Working with Errors.