Can't paint picture in Jesse's room

I have been trying to finish painting the grass in the picture in Jesse's room and it won't let me paint it. I have the big area of grass already painted and the little areas that are suppose to be a light green won't let me paint it. They were painted the dark green along with the other grass, but when I go to paint it the light green it says that I used the wrong color. Does anybody know what I have done wrong, or what I need to do to get this painted. I can't move on until this light patch of grass is finished. Please help me somebody.
Janice Fredde

Im having the same problem as you.

Any luck?