Hi Alexandre,
You must use color 16 for transparent background. This way the user can choose underlying brick color to get the appearance of a fully transparent sticker. Using sheet number (820674a, 820674b & 820674c) is the way to go. See specif. here http://www.ldraw.org/article/339 (though I must admit that the paragraph about color 16 is not extremely clear to me...)
You must use color 16 for transparent background. This way the user can choose underlying brick color to get the appearance of a fully transparent sticker. Using sheet number (820674a, 820674b & 820674c) is the way to go. See specif. here http://www.ldraw.org/article/339 (though I must admit that the paragraph about color 16 is not extremely clear to me...)