Can metal ball casters be covered?
You might like "caster cups"



You can get them in a variety of colours, sizes and materials including transparent plastic.



For chairs that need to be slid in and out from under a table, you might need a type of caster cup specifically intended for that purpose


  The only castor cup where the wheels stay in the cup when furniture is moved


- From advertisement for "MagiGLIDE CASTOR CUP 4 PACK". I have not tried this and don't know if it is suitable for the intended use or whether the claims are justified.

Castor cups are usually cheap - it doesn't hurt to try them on one chair. You don't lose much if they turn out to be unsuitable.