How to understand Aposematism and Batesian mimicry
I could be misreading your question, but it doesn't sound very specific. Rather, it sounds like you're asking "How can I make sense of all the various color schemes employed by venomous species?" So I'll take a stab at it...

Animal coloration is a very complex phenomenon, with a number of overlapping physiological traits, evolutionary strategies, etc.

Consider the famous relationship between the monarch and viceroy butterflies, which bear a striking similarity. The viceroy was long regarded as a harmless insect that predators avoided because it resembled the monarch, which many predators find non-appetizing.

More recently, it was proposed that the viceroy is also unpalatable. Thus, the similar color patterns may simply reinforce each other. (Mutual Mimicry: Viceroy and Monarch)

But that's just one isolated example of a bewildering spectrum of color schemes. Some animals apparently use bright colors as a warning - "I'm toxic!" - while other venomous species may be dull colored for whatever reason. A dull-colored species may use its venom to capture prey, which it captures in ambush; thus, it has evolved camouflage, rather than conspicuous colors.

Coloration is also about more than warning. Coloration can serve as a means of communication. It can help a member of a species recognize fellow members. Bright colors are very popular in mating rituals.

So you have all these overlapping traits and countless unique evolutionary experiments interwoven into a can of worms.

One example that comes to mind is venomous snakes native to the United States. The rattlesnake and cottonmouth are pretty drab-colored and generally well camouflaged. Of course, rattlesnakes warn potential enemies with their famous rattles. I think the cottonmouth can be considered fairly drab colored as well.

However, the coral snake has a very vivid and distinctive color pattern. And there are snakes that bear a remarkably resemblance to coral snakes (see some examples).