How to distinguish syntax highlighting between function and argument?

[shirdekel]

The syntax highlighting for test(var1) in the following code doesn't distinguish between function name and the argument:

function("var1")
function(var1)
test("var1")
c(TRUE, FALSE)
test(var1)

I expected there to be a different colour between the function and the argument (as in the screenshot here).

I got the same results with different themes and after turning semantic highlighting on and off.