I'm trying to figure out dragons my self. . . not in theory but facts. Since I can't breed as I did in the past, I have to figure them out by looking at other people's results.
Theoretically, metallics are single metallic while dragons are double metallic . . . at least that's what I read (somewhere). But I'm not really concerned about the theory. I noticed that color combo works a bit differently on them. Yellow for example is physically brought out easier compared to regular colors.
I don't now how to explain copper, copper dragon, and steel blue dragon as I don't know the theory behind them. But I do know they exist. I've seen and even had them. Copper dragon (the one I had) was more grey than copper. Copper metallics have a tint of red on them that make them look copper. These copper dragons commonly come in black dragons. When crossed to red dragons they may produce silverish/grey body with red fins. . . . not sure what to call them. I haven't had the chance to cross them to other colors.
Steel blue dragons look rather dull compared to the turquoise/green and the blue dragon. I have never produce royal blue when crossing the two colors. I only got more steel blue and green which came in different shades - from dull to bright. . . . this differs to regular colors . . .
In regular color green x steel blue will produce royal blue. But on the other hand breeding a blue dragon to platinum will produce some steel blue. . . . don't know how that works in theory. I'm guessing this is due to the platinum's genetic background being steel blue.
In theory steel blue genes is responsible for copper, platinum and steel blue dragon. The best logic I can think of is the total genetic make up. In order to physically be those colors, they need specific genetic combinations. . . . white, for example, is royal blue x cambodian(NR). But white will not always appear. They need that specific combination to be white. So I guess the above colors too need similar combinations.
Your guy seems to have white, blue, and yellow in him. So if you breed him, those colors will take part in determining fry color. If you want clean white bodies, like dragons should be, I suggest not breeding him to a copper. (You might get grey body). Breed him to a white body dragon or irid dragon.
Sorry I can't explain it better. Please share what ever you breed him with so we can all learn how these color works.