Hi Goddess Tsunade. I think the yellow colour is actually the correct colour. The way the lava looked at the kage summit (red/orange and viscous like actual lava) was a mistake in my opinion.
If you look at the below image, the lava is thin and watery. Its not really lava in my opinion, more live a liquid version of Mei's boil release - some sort of chemical liquid that disolves whatever it makes contact with. This new lava in the latest shippuden episode reflects this. Also if i'm not mistaked, another translation for yoton is melting/dissolve style.
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Also if you look at this picture, Mei's lava doesnt look al that fiery. Its light coloured with some darker coloured outline.
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I'd also like to point out the different japanese kanji used for lava. In Roshi's case - 熔, using the fire (火) radical. In Mei's case - 溶, using the water (水) radical.
熔 - associated with solids, fusing and melting. 溶 - associated with liquids, soluble and dissolving.