To give you more color ideas, here are images from previous Tyranid codices (download for full resolution): The color of Tyranid biomorphs, which are biomechanical devices and evolved genetic mutations that give a Tyranid fighting advantages on the field against enemies, are also colored uniquely among Tyranid armies. The bioforms of Hive Fleets have unique color schemes, but may differ in color tone and hues. Hive Fleet Ouroboris – desaturated, or light colored brown flesh skin with green carapace armor.Hive Fleet Leviathan – pale, white-tone skin with tints of pink and purple armored carapace biomorphs are red.Hive Fleet Kronos – black or dark-toned skin flesh and a reddish, warm hued armor carapace.Hive Fleet Kraken – pale, beige or neutral flesh tone with red armor.Hive Fleet Hydra – purple or dark violet skin flesh and dark blue or black toned armored carapace.Hive Fleet Gorgon – green flesh skin with pale, beige armored carapace.Hive Fleet Dagon – similar to Hive Fleet Behemoth.Hive Fleet Behemoth – red flesh and blue toned carapace armor.Here are the Tyranid Hive Fleets in the Warhammer 40k universe with their unique and basic color motifs (may not be official Games Workshop colors):
Use the Games Workshop colour schemes, mix and match, or find inspiration for an alternative Tyranid color scheme. For simplicity, I categorized them into 9 color motifs.