[talanum1 (OP)]

Why are Jupiter's gasses not mixed into a single even color?

[chiralSPO]

Probably similar reasons that the Earth has cloudy parts and non-cloudy parts of the atmosphere.

There are differences of course, but the underlying physics (and/or chemistry) is the same: there are differences in temperature and pressure throughout the atmosphere (and to a much greater extent for Jupiter than here!), and that leads to changes in phase (solid/liquid/gas/plasma) for the various components in the atmosphere, and that leads to local changes in composition (ie precipitation), as well as weather patterns (Jupiter has some very impressive storms, polar vortices, and jet streams). The belts and zones on Jupiter are a manifestation of the jet streams.

See more: https://en.wikipedia.org/wiki/Atmosphere_of_Jupiter

[Europan Ocean]

Perhaps the gravity separates them by weight and density... Only later are they stirred up by storms, and currents.