How can I remove "segment-left-yellow.png from start up programs?

OK .. your startup services (daemons) are controlled by a system called launchd and in effect are a series of files located in your user:Library:LaunchAgents and in the root system Library folder in the LaunchAgents and LaunchDaemons folders

You can manage the daemons from the command line (from Terminal.app under /Applications/Utilities/) or by using a tool like Lingon or LaunchControl
http://www.macupdate.com/app/mac/19879/lingon
http://www.macupdate.com/app/mac/46921/launchcontrol

You can also open a terminal window and run the following command
launchctl list

There will be a LOT of services listed so you might have to look carefully to see if any

To remove a service you simply type
launchctl remove ******
where *** is the full filename of the plist you want to get rid of

Another clue might be to restart your computer and let the pop-up appear
Then open the Activity Monitor application and you can see a list of all running services and windows
Hopefully you'll see the name of a strange program or process which is the plist you can look for in the folders I indicated and REMOVE it

Thanks for the comment.  I looked at the window that opens when I launch more closely.  The window is actually a Preview window displaying the yellow color swatch.

I opened the Terminal.app and ran the lauchctl list command.  I did not see anything with "segment-left-yellow.png".  

I did see  a line with com.apple.Preview.7894

I wonder if this is the line causing Preview to launch.

If I delete the line with the launchctl remove command and it is not the source of my problem, how do I reinsert the line into the launchctl list?

Did you look at the plist files in your user:Library:LaunchAgents folder? This is the most likely location for the rogue startup plist.
You will NOT see a process or plist with "segment-left-yellow.png" as it is an image file and you need an application or other process to display it and this is what you're trying to track down.
Did you open the Activity monitor after the Mac starts up?  See if you can highlight and kill processes and you might spot the one which is loading the png file.

~/Library/LaunchAgents #Per-user agents provided by the user.#
/Library/LaunchAgents # Per-user agents provided by the administrator#
/Library/LaunchDaemons #System wide daemons provided by the administrator#
/System/Library/LaunchAgents #Mac OS X Per-user agents.#
/System/Library/LaunchDaemons #Mac OS X System wide daemons.#

Before you go removing plist files using the remove command.  Check also the StartupItems folder in the Library folder inside your user home folder.
Also open the system preference application. Go to your user and look under the Login items section for your user and see is there anything in there which you'd not expect.

Basically when your Mac starts up what programs are opening? One of them is loading that png file. Before you assume it is Preview have you stopped or quit that application and the png disappears?

Okay, I looked at the files in user>library>launchagents - I couldn't spot anything.

I opened Activity Monitor - I found the Preview process, double clicked to open it - the parent process is launchd(1).  When I kill the process, the Preview window displaying the yellow.png closes down.

So I can find the Preview process and manually close it.  

I still don't know how to stop it from launching when I boot up.

Wanjo
Did you try the other routes and check your startup items and login items in system preferences?

I just went into login items and system preferences.  There are only 2 times in there.  The first one is "segment-left-yellow.png".  I unlocked login items and clicked the "Hide" check box.  I then rebooted.  Segment-left-yellow .png is still launching in Preview??

I went back through user>home>library>startup - the folder is empty.

I give up!

Problem Solved!  Thank you for your expertise and patience!

eoinosullivan worked me through the problem step by step.  He was patient with me even when I was frustrated.  It took several attempts.  In the end, eoinosullivan was able to lead me to the solution.  A+++!