You can use the stylesheet to customize the color of nodes (representing the values ?s and ?o of the query).

The patterns to apply styles are defined as follows:

Same style for both variables:
    bind(\"<key>\" as ?style)

Style for variable ?s:
    bind(\"<key>\" as ?style1)

Style for variable ?o:
    bind(\"<key>\" as ?style2)

Second style of variables:
    bind(\"<key>\" as ?mix)

Example of application using the default stylesheet:

select * where {
  ?s ?p ?o
  bind ("fst" as ?style1)
  bind ("snd" as ?style2)
  bind ("rst" as ?mix)
}