Id= Inhibitor of Dermal melanin. Green is yellow skin plus melanin in the dermal layer. just to be repetitive as sometimes it helps to click it in more- blue is white skin plus melanin in the dermal layer. You got it- get green by crossing the blue leg boy with yellow legged girls- if he;s het Id, you will get half green legged girls(with the other girls being blue legged) you could think of no Id that way... I think of it as being the ancestral trait- the default, with Id being a dominant and sex linked mutation that showed up sometime during domestication.