Simple basic black finishing is pretty easy with aerosol primers and trim black. Personal preference for something basic is Spraymax 3680405 black primer and 3680101 gloss trim black. (3680102 satin and 3680103 for matte). Second best option would be SEM aerosols of 42003 black primer and 49153 gloss trim black (49143 for satin or 49133 for matte).
These aren't fancy cans equal to what I'd recommend for long term on your speakers, but they'll work well enough and look clean on your bases without too much trouble.
As for protecting bases and speakers and floors, you could look at herbies dots, go the isoacoustic orea pods route, or even just some modeling clay to keep speaker from sliding on the bases. As for bases to floor, maybe some furniture dots for cheap or Gaia pods? You won't want double isolation devices used, but isolating at the floor or at the speaker is not a bad idea.