The Chinook in the picture is a red.  Blunt nose = red.  That is the first thing I look for during the split second decision of "do I release it...or bonk it?"  Fish has to be prime chrome shape.  Or it is getting released.   I have caught marble Chinook before, they are nice fish for the barb-e-que.  I have heard a theory or two.  Some say the marble Chinook has such a color because of what they eat.  More shrimp = more red???  Some say it is the red Chinook cross bread with a white Chinook.  If that is possible or not.  I catch a few marbles on the Vedder every year in early september.  You can't really tell until you gut it and fillet it that it is a true marble.   The only indication I can see is they are in allot better shape (chromer) then the whites.  I keep one white every year to make fish and chips with.  Fillet it, cut it into smaller pieces, batter it up, a little tarter sauce, and you can barely tell the difference between a piece of cod.