Custom Tileset edge problem

[hwane9595]

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I put in the Gradation to Photoshop, but still can see the edge between the tiles.

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Somebody said to me:
"The edge problem is simple. Just put it in the Gradation from alpha. (Photoshop)then you solve that problem."

The method I used is:
1. Create the New Layer in Photoshop
2. Choose the color with Eyedropper Tool (Spoide Tool)
3. Fill up the Layer before I choose that color with Gradation Tool
4. Control the Opacity

Was something wrong or missed I before?