Question: is there a command line utility for changing the color label of files in macosx?

Answer: 
You can write it yourself. Open `/Applications/Utilities/AppleScript Editor.app` and enter the following:

```
on run argv
    tell application "Finder"
        set theFile to POSIX file (item 1 of argv) as alias
        set labelIdx to (item 2 of argv as number)
        set label index of theFile to labelIdx
    end tell
end run

```

Save as `color.scpt` and invoke from Terminal like this:

```
osascript color.scpt somefile.txt 3

```

`somefile.txt` will be colored, `3` is the color: `0` means colorless, 1 through 7 are the Finder's colors (with `1` being red).
This article, [View and set Labels from the command line](http://www.macosxhints.com/article.php?story=20031030221241557), describes a command line utility to do it. Caveat: it's an old article, describing a utility for OS 10.3, and I haven't tried it myself.