Things You'll Need
Instructions
Open UnLZ-GBA by double clicking its icon.
Click the "OpenFile" button and select your "Pokemon LeafGreen" ROM.
Find the Venusaur tile set that functions as the title screen. It will most likely be at position 2011.
Click the Venusaur, then click the "Save As" button and save it to a convenient place. This will save the title set to your computer.
Open the Venusaur tile set picture in your paint program.
Use UnLZ-GBA to save the sprite of the Pokemon you want on the title screen to the same place as your Venusaur.
Open the sprite in your paint program and recolor it using the gray scale palette you saw in the Venusaur picture.
Click back to the Venusaur tile set and delete the Venusaur from the picture.
Copy and paste the new sprite into the Venusaur tile set. Make sure it goes into the exact same place as the Venusaur was.
Save the tile set as its original size.
Go back to UnLZ-GBA then press the Import button.
Select the Venusaur tile set and press "OK".
Press the save button.