The top of the spreaders and the top portion of the masts are painted white because they are harder to re-varnish. A quick coat of paint is easier and more durable.
You don't notice the top of the spreaders unless you go aloft.
There is a tide in the affairs of men,
Which, taken at the flood, leads on to fortune;
Omitted, all the voyage of their life
Is bound in shallows and in miseries.
Shakespeare, Julius Caesar IV, iii, 217