what i have seen and heared is that like with yellowbelly, its mostly seen near the belly. not as busy and random as in YB, but with black lines near the belly, railroad tracks, some randomness. and on its own, spark is, how can i say it, stronger than specter.

i guess its most easy for the breeder to identify since he/she has experience with the morph and has seen many clutches with it, and with just pictures, or with just one BP and no clutchmates and no parents to look at and compare to, it gets really hard and iffy.