@renandesouzaIts hard to tell the quality from the preview but it looks nice from the preview picture in the forums. The back yellow picture should be recolored not set behind the transparent yellow layer in the template. The yellow layer is just there to remind you what color to use on the back. I know the back pictures you have look nice but always use 300dpi images.

To quote myself here are some helpful tips on recoloring the back yellow and the spine green.
Its really simple, first off you'll want to duplicate your "spine layer" just in case the new colored spine isn't perfect you can give it another shot.
In Photoshop:
Image => Adjustments => Gradient Map...
Then a little colored box will pop up. Click the area where the colors are and a new little window will pop up. In this new window there are little selectors where you can choose a new color. You will only need three selectors (one on the far right, one in the middle and one on the far left).
Far Left (Dark Green)
if you want to go into greater accuracy you can mimic my exact colors i use.
When you click the far left selector to choose a color you can enter color values (numbers).
R: 20, G: 61, B:18
Middle (light green)
R: 71, G: 192, B: 82
Far Right (white green)
R:196, G: 255, B: 184
That was kind of the advanced version but its not too hard to figure out 
[k nice that looks great on mine but what did you do for the yellow?
Same step as before but the selector are in different locations. You can fidget around with these a lot more loosely than the spine colors. I often move the selectors around until i get it just right.

Left:
R: 231, G: 109, B: 0
Middle:
R: 255, G: 234, B: 0
Right:
R: 253, G: 249, B: 189
EDIT:
I've been thinking for a while that i should group together all my suggestions that i have been giving members into a guide or FAQ. Maybe even a cover making 101. Problem is that would take a huge amount of time. What do you guys think is more important, me making a guide or a bunch of covers? PM me with a response (lets not clutter up this thread). 
EDIT:Maybe i'm just in a helpful mood today

Try this link out for a filtered new yellow back for you. Its still the same image but with the filter it creates a blur on purpose and the image is 300dpi this way. I've done this for quite a few of my back images.
http://www.box.net/shared/q9dreivc6q