The first Harry Potter book was published in 1997. In 1999, the novel Game of Thrones was published, and the world was introduced to House Lannister... which bore Gryiffindor's symbol and colors. But the Lannister's are the antithesis of Gryffindor and make the worst Slytherins seem like petty mischief makers.
And sometimes I can't help but wonder if Martin deliberately chose a Lion and Red and Gold as the symbols of House Lannister in order to furthur remind people that his is not a world where symbols match character and that the themes of Harry Potter won't get you far here. In fact, Martin even said that he found a way for the symbol and colors to be used in negative lights. The Lion and red represents the Lannisters wanting to be seen as royalty and thus powerful, while Gold represents their greed and riches.
But do you think he picked that symbol and color just for that or do you think he got a few ideas for deconstruction from Harry Potter?