But the section you refer to is about constructing sequences from atomar values, there you need () to construct a sequence. Your example however uses an XPath expression with an element name as a node test and in XPath 1.0 that results in a node set why it is my understanding that in XPath 2.0 it results in a sequence of nodes.
Indeed if I try the example with Saxon 7.5 without the () around color then the result is the same as with (color).