I already said it looks lot more better than the grey without colors
Make me remember all the first Next Gen gameswhere people in industry maked all games grey or very dark to avoid taking risks !
Only keep these colored textures. For Lava you don't need thousand of laval texture, you have already one.

For Water just modify it a little and put a blue color.
Simple textures patterns like that are not so extravagant in terms of Work ? or i'm wrong ?

Just make some variations on colors or patterns above the basic texture to make textures for next levels !
Its perfect, keep it simple !