You likely used a slightly different shade of pink. Ensure your RGB is exactly 255, 0, 255.
A 1-pixel black border around your main icon helps it stand out against the varying colors of game maps. emblem ragnarok 24x24 bmp
Transparency in Ragnarok Online doesn't use alpha channels like a PNG. Instead, the game engine looks for a specific "Color Key." You likely used a slightly different shade of pink