Limitations to covering an existing tattoo

I have a tattoo on my arm that has faded and degraded to the point that only I can tell what it is anymore, it really wasn't that clear to begin with. It is primarily black with some red and a slight line of yellow. Are there any limitations to how I can cover this? Will certain colors not cover? Any tips would be appreciated.

No way to give you an answer without seeing the tattoo first...e-mail it to me!

Thanks for the reply, I sent an e-mail with a picture of the tattoo to the link you provided.