Turn off floaters until you can see the canvas.  Press Ctrl + A to select the background.  Change to the Floater Adjuster Tool if it isn’t already selected and click on the background to create a floater.  Name it Ambient.  In the Art Materials palette choose white for your Secondary Color and black for your Primary Color.  Select Grad/Two-Point/Mirrored Right to Left Grad (32).  Move the red ball around the circle until you have a reading of 27%.   Select the Fill Tool.  With the Ambient selected click once inside the image.  If you have Fill With Grad selected you will have something like this (33). 

In the Art Materials palette choose a light yellow-green for your color.   Click once inside the Ambient Select the Floater Adjuster Tool.  In the Contols Brush: palette set Opacity at 12%.  Your picture should look like this (35).