How can you visually tell the difference of softwood?

The appearance of softwood is much like any other wood to the layperson, weight can generally give a person some indication, (with some exceptions) usually hardwoods are heavier. This site explains a lot about this subject:

Appearance Lumber (Finish, Selects) Appearance lumber (graded as Finish or Selects) is often nonstress-graded but a separate category exists due to the greater importance placed on appearance. Boards in this category will be of most use to the woodworker interested in making quality softwood furniture with a natural finish. In addition to boards, this group includes most softwood lumber that has been custom milled to a pattern or otherwise surfaced on all four sides (S4S). Examples are trim, siding, shingles, flooring, casing, base, stepping, and paneling. The highest grade of appearance lumber is Finish, which is subdivided into grades composed of letters or combinations of letters (B&BTR, C, D) or names such as Superior or Prime, depending on the grading agency. The next level down is Selects which has grade designations composed of numbers, letters, and names of combinations of them (B&BTR, C Select, D Select). * http://www.woodbin.com/ref/wood/softwood_grades.htm