I was exploring around a Jungle on a Minecraft 1.16.4 server and I had encountered a jungle vine that had appeared to be blue. The specific biome is a bamboo jungle and this tree is directly next to a warm ocean by a couple of blocks. I can assume that this is a visual glitch with the biome blending mechanics making the vine appear in this color, other than a visual texture, the vine does not behave in any other way. But I thought it was interesting enough to share here. So far, I have only found one other post about this on the internet on reddit with someone encountering the same situation. Hope this helps.