Depth per color of lead line?

[MeredithMan]

Any ballpark correlation of color of lead line to depth? For example, every color equates to 5' of depth, so if fish are showing at 20', let out 4 colors' worth of line? Is it that simple?

I do have a fish finder, but no downriggers, so looking for a "model" to get close to the depth they might be showing at.

Thanks!