The official Pokémon HeartGold and SoulSilver website announced that the Pikachu-Coloured Pichu event will now be available in Europe via Nintendo Wi-Fi Connection. This is the same Pichu that was given out at Gamestop in the United States and it is now also available via Nintendo Wi-Fi Connection. The Pichu will be available for download through the Mystery Gift option in Pokémon Diamond, Pearl and Platinum versions from March 5th, 2010 to March 25th, 2010.

This Shiny Pichu is a deeper yellow colour than most Pichu and it has bright red cheeks, much like its famous evolved form, Pikachu! When Pokémon HeartGold and SoulSilver are released, player will then be able to transfer the Pikachu Colored Pichu from their Pokémon Diamond, Pearl or Platinum Version. Players can then take Pikachu Colored Pichu to Ilex Forest (ウバメのもり) where Spiky-Eared Pichu (ギザみみピチュー) will join their team.

Source: http://www.pokemongoldsilver.com/uk/shiny-pichu.html